Too much music? Wish you could split your collection into two (say, a laptop version [small] and a failure-resistant network-attached storage device [all music ever recorded], for instance)?

One Mac OS X Hints user developed a script to switch between two aliased drives to accomplish this task. Even better solutions are presented in the thread below.

Update 12/17/2006:

With iTunes 7, switching between different music libraries became much, much easier. If you hold down Option (or Alt in Windows) while launching the application from the Dock, you will be presented with a dialog that lets you switch between different iTunes libraries. You can also create new libraries from this window, choosing either your local hard drive, an external device, or even a network drive.

It seems that with every iTunes update, the really good stuff is much less publicized.