While browsing the file system from the Terminal the other day, I discovered that the Trash folder at the top level of my Start up disk contained 250Mb of files in "Rescued Items from HD" folders. This disk contains my Classic System (OS9), although I never boot OS 9 from this disk, so I can only assume that when the Classic Environment crashes and is restarted, it still saves useless rescued folders to the (now invisible in OS X) top level Trash directory just as it did in OS 9. In OS X, trash is separated for each user and resides in their home directory.
If you use Classic much and need a bit of space, it may be worthwhile to periodically empty this directory. For those unwilling to use the Terminal, the top-level trash can be emptied from applications like Xupport.
[robg adds: From the Terminal, you should be able to use sudo rm -r "/.Trashes/Rescued Items from HD" to get rid of this folder.]
One of the many things I hate about OS X is embedded Command-Tab switching. Come to think of it, I hated it in OS 9 as well. Before all of this 'digital lifestyle' business my primary use for my Mac was as a production machine at work running Quark in which Command-Tab switched between tools on the toolbar. Why Apple has been so fanatical about embedding Command-Tab switching into their operating system I will never understand. Anyway, I have two tips for stopping the Command-Tab problem once and for all, for those grizzled old-school Quark 'power-users' who care.
For OS X, my favorite solution is PullTab which has been mentioned elsewhere, availabe for free. It does, however, require the installation of Unsanity's Application Enhancer (also free). PullTab seems to effectively kill Command-tab switching in all of OS X.
In OS 9 or Classic, the problem is more involved. As far as I can tell, you must boot your machine into OS 9 first and then access the Mac Help Viewer, do a search for 'Switching between open programs,' and on that page is a link (towards the bottom) that will launch an AppleScript which allows you to change the keyboard shortcut the Application Switcher control panel uses, or to disable it completely.
Alternatively, you can run the AppleScript directly and skip the Help Viewer altogether. The script is located at /System Folder -> Help -> Mac Help -> fp -> shrd -> SetKeyboardSwitching on my machine.
Some may be tempted to access the OS 9 help viewer from Classic while it is running under OS X. I was unable to get the required AppleScript to run under these circumstances, but rebooting into 9 solved the issue. That's it, few may care but those who do and are stumped I am sure will appreciate the info.
Many inkjets (and non-PostScript laser printers) can be networked in OS 10.2.x using ESP Ghostscript and one of the driver packages from the Mac OS X page at LinuxPrinting.org, and using either a cheap ($50) parallel to ethernet print server, or even a router that has a built-in parallel port print server.
I could not, however, figure out how to print from Classic to a networked inkjet, since Classic uses the OS 9 printing system, not the CUPS system used in OS 10.2.x. Trying to print directly from Classic gives pages of junk printing. But I found at least a partial solution (note: this assumes you have already set up the printer in OS X):
Set up the inkjet in Classic as a LaserWriter 8 LPR printer using the OS 9 Desktop Printer Utility.
In Classic, print to a PostScript file instead of to the printer.
Drag the PostScript file from your desktop to the OS X Print Center. It will print on the default printer.
Read the rest of the hint for a detailed version of these instructions...
If you've set Classic to start at login, you probably agree that the Startup window gets in the way. This hint will explain how to make Classic start without displaying anything. Also, for some reason, it makes Classic start a little faster!
One of our clients needed a copy of Classic on their XServe (for Cumulus purposes) , but it was impossible to install it. I found out that it had something to do with the Danish version of the Mac OS 9, we were trying to install. Mac OS X server only comes in four languages (English, German, French and Japanese) and Classic must be one of those languages.
I tried everything but to no avail, and at last I came up with a not so obvious solution:
Get the NetBoot (Mac OS 9) CD that comes with the XServe.
It seems that Classic applications cannot access IP services if Internet Sharing is enabled.
[robg adds: I took one for the team and fired up Classic for the first time in months ... and this appears to be true! When Internet Sharing is enabled, IE 5.1 in Classic cannot load any sites. Disable sharing, and (even without a Classic restart), IE 5.1 loads all pages fine. Anyone know a workaround?]
PROBLEM: Is there a way I can remove Classic from my OS X system? I don't have system 9.x installed, but the Classic pane is still in my System Preferences.
SOLUTION: When people say they want to "uninstall" Classic, what they may mean is that they want to disable the System Preferences "Classic" pane. If you don't have an OS 9 install at all, or OS X is installed on a UFS partition, Classic won't start up anyway. Simply remove the /System -> Library -> PreferencePanes -> Classic.prefPane file, and that's the last you'll see of Classic again. You'll need to have root-level privileges to do this, of course.
[robg adds: As a caution, you may want to think twice before doing this -- the possible implications on future Software Updates that may try to update Classic resources is, of course, not known. More than likely, the updater would just install entire components, but personally, I prefer to leave as much of my system in 'stock' mode as possible to minimize potential upgrade difficulties. That warning aside, read the rest of the hint for info on how to remove the rest of Classic support from your machine...]
I'm still hamstrung by old graphic files from OS 9 / OS 8.1 in lots of different formats, such as ClarisDraw. I still use these documents because they have value, and there's a lot of inertia to convert some of them into Illustrator. Yeah, I'm lazy!
So I've been trying to figure out how to convert these files to Illustrator 10 in an editable format, so I can still optimize and edit objects etc. in OS X, and never have to run Classic again. Well I've found a way, and I'm not sure it's been published here so here it goes. First, the downside, you'll need Adobe Acrobat 5 (not Acrobat Reader), your original OS 9 graphic software of choice, and an OS X graphic application as well. I used ClarisDraw with Illustrator and Freehand in this test.
Start Classic, make sure all your printer extensions are enable such as Laserwriter8 and desktop printer spooler etc. Restart Classic if they're not.
Go to the Applications -> Adobe Acrobat 5.0 -> AdobePS folder. Start up the Desktop Printer Utility and assign a new desktop printer using Laserwriter 8 and Translator (Postscript). You'll then see a dialogue box indicating the PPD file (printer description) and destination. I left them as is, and simply clicked on "create" and assign a name to the printer, in my case "convert".
Now start up your Classic graphic app. and load up your file, simply print and choose the new "convert" printer, your file will be saved at your set location.
Go to Illustrator in X, now open your file with its .ps extension. Voila! You now have a graphic file which you can manipulate and edit in Illustrator.
I only found one file (out of 25) which didn't convert 100% well, and the difference was so small as to be insignificant.
I know this is probably a very unique problem I had, and pertains to a small percentage of users, but it would be interesting to see if other users can do this with old figures/graphic files on antiquated formats.
OK, big Classic startup problem on my 800 MHz iBook. Hit 'Start'. Get instant '...failed ' error message. Boots OK from OS 9 so that's not the problem. Standard select OS 9 startup disk, start classic, reselect OS X startup disk fails because Classic cannot start. Disk Utility - Repair Permissions. No help. The logs in Console talk about trying to load something past end of file - sounds like corruption to me. Sometimes it gives  as the error code instead.
Occasionally in Jaguar (10.2.2), Classic goes screwy--very very screwy. Mouse clicks start to bomb applications, and may crash Classic and (twice in my experience) do Very Bad Things to OSX itself. Fortunately, there's an easy fix.
When mouse clicks start to go bad, load up the OS X system preferences panel and select Classic. Without doing anything else (leave Classic running), choose Rebuild Desktop. This seems to restore sanity to Classic without any further ado.
[Editor's note: I haven't had any such problems with 10.2.3 (yet?), but then again, I seldom run Classic any longer. If you do and you've had problems, please post if this hint helped resolve your problem.]