If all you want is the apps you can save the ipa files but you can save all itunes stuff fairly easily but it is more involved than just saving one folder.
Steps are for windows and similar on mac I believe, this took me a couple moves to figure out but I have it down now. For moving to a new computer or simply reinstalling windows on same computer.
1. On the old computer do Preferences -> advanced -> Keep itunes media folder organized. This could take a long time if you weren't doing it. Also make sure your disk is big enough to suck in all your media files.
2. Find your media folder, mentioned on the same screen above.
3. Find your library folder, if you hold shift and launch itunes and click the choose library button it will likely show you the folder you are using. Otherwise http://support.apple.com/kb/ht1660
4. Consider deauthorizing the old computer in itunes if you are never going to use it again.
5. Move both the library and media folders to the new computer. Media folder should have the same directory path otherwise hard links in library may have trouble.
6. Shift launch itunes and point it to your library file iTunes Library.itl.
7. Everything should be as it was on the old computer.
8. Authorize the new computer.
I've transplanted the library from Windows to Mac. MaxBurn's post is pretty much it, except I went through the extra step of editing the library XML file and updating the folder names that everything was pointing to with a quick find/replace (on Windows, they have a drive letter). Everything else was in the same logical location besides the drive letter (C:/Users/fury/Music/iTunes... vs. /Users/fury/Music/iTunes...) which may have helped the process, but any find/replace to point to the proper file system location should do..