This is a known hint, but Tiger has one important change to the process and I think it worth of mentioning again.
Almost all Apple's application are localized for different languages. I don't need any except English, so removing those localizations can save a lot of space on your hard drive. When I say "a lot," I mean it -- we're talking about hundreds of megabytes and tenth of thousands small files, which are a real burden on any file system. I cleaned my Applications folder, and this saved me over 500MB just on applications like iCal, Safari, Pages, iTunes, DVD Player and others.
Tiger has a nice improvement here and makes the process a lot simpler. Just do a regular Get Info (Command-I) on any application and look for the Languages section. If you expand it, you'll see all languages the program supports. Now if you need only the English localization, hit Command-A for "Select All," and then hit the Remove button. English is grayed out and you cannot remove it this way, so all the othes will be removed, leaving English. The Select All in Get Info's Languages panel didn't work with Panther, and it was a lot more difficult process.
This is officially supported and very basic functionality of Mac OS X 10.4. It should be safe, but just in case -- back up the applications before modification, and keep them around while testing the modified version.
[robg adds: There are a few hints here on how to do this in previous versions of OS X. There are at least two third party tools that have gotten good reviews, too: Monolingual and Delocalizer. I don't know which, if either, work with Tiger -- Monolingual was updated in May; Delocalizer hasn't been updated lately. Needless to say, please backup before you try one of these apps or this hint...]

