I've never seen this before, so I'm guessing it's new with 10.4. In any program that has a 'Window' menu, you'll find "Bring All To Front." However, if you hold down the Option key after opening the menu, this becomes "Arrange In Front." Select it, and you get a (nasty IMO) Windows-esque cascading arrangement feature.
Not much of a hint, unless you like that sort of thing!
[robg adds:Yikes; I'll make sure I never hold down the Option key on the Window menu! One of the things that makes this feature so disconcerting is that it also reorders your windows -- regardless of which window was active, it seems to bring the oldest window to the foreground, then cascade the rest behind that one. It's very confusing, especially if you've got a lot of open windows (I tried it with about 15 TextEdit windows open). I'm personally glad this one's hiding behind the Option key modifier!]
Mac OS X Hints
http://hints.macworld.com/article.php?story=20050519021838783