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.]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20031008105019189