The problem we were having was that users didn't have write permissions to other people's files, meaning that different users couldn't collaborate on common files, without the original creator changing the permissions manually. Yes, we could have used BatChmod or set up a cron job on the server to change the permissions for us on a periodic basis, but this was not transparent enough. What we wanted is that the Finder (and any other applications) created new files or folders with read and write privleges for all users. There had been a fix which worked for 10.2.x, but this got broken by 10.3, and the search has been on since then for a new fix.
Marcel Bresink has implemented a per-user umask Preference in the latest version of his TinkerTool 3.1, allowing individual users to change the defualt permissions on their own files. If this is what people want to do, I would highly recommend they use this utility as it makes the whole thing so easy.
For those who want to set it on a global basis, so that it applies for all the users of a computer, read on.
Side note: This still works in 10.4...
I had seen a posting by Xsage on a mail group highlighting the presence of a NSUmask default hidden away in the file /System -> Library -> Frameworks -> PreferencePanes.framework -> Versions -> A -> Resources -> global.defaults. The default NSUmask has a value of 18, which is the decimal equivalent of the octal umask setting 022, and is the global default. Since changing the permissions that the System runs with can cause all sorts of nasty things to happen, particularly if you want to set a more restrictive umask than the normal default, we would ideally look to override this default somewhere else.
TinkerTool implements this on a per-user basis by inserting an NSUmask override setting in the file ~/Library -> Preferences -> .GlobalPreferences.plist. The inserted lines are:
<key>NSUmask</key>
<integer>my-umask-decimal</integer>
Replace my-umask-decimal with the decimal conversion of the octal umask you want to set. A decimal NSumask of 0 gives the octal umask value of 000 that I required. To implement this change on a global basis, we simply insert the same setting, but into another file: /Library -> Preferences -> .GlobalPreferences.plist. I have just been putting it right at the at the top, for example:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple Computer//DTD PLIST 1.0//EN"
"http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
<key>NSUmask</key>
<integer>0</integer>
<key>AppleLanguages</key>
<array>
<string>English</string>
And that is about it. Obviously you will need to have administrative privileges to be able to do this, and you should save a backup of any files you change etc, etc. As an aside, the global.defaults file contains a few other interesting things that other people might want to mess with, including mouse scaling and key repeat times.

