I'll start the ball rolling...
You've got three default font folders, located at /System/Library/Fonts, /Library/Fonts, and /Users/Your short name/Library/Fonts.
Mac OS X 10.5: Fonts list (There doesn't appear to be a similar doc relating to OS X 10.6, but I expect that the principles remain the same.) offers some insights into what you may and may not do with fonts in the first two locations.
Also as a general rule, you can trash any font in the third location, but be certain that you know precisely what it is and why it's there before you do the dirty deed.
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If I "disable" fonts, is that equal to "remove"?Disabling a font does
not delete it.
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Is it enough to disable fonts from Applications?Ain't no such animal...sounds like you may be talking about
deleting language localizations; you'll find some discussion and suggested tools
here. (Deleting localizations, both in apps and OS X, itself, can free up a nice chunk of space for you.)
Hope this helps for starters.