For reasons unknown, Apple makes it really difficult to move around one's iTunes library.
Just moving the library to another hard drive will result in all the files being disconnected. Unlike Aperture or Final Cut Pro, there is no automated path fix. If you want to correct the paths you have to do it file by file.
There's also a hidden function inside iTunes which is really deadly (I believe it comes turned on by default) to reorder your library. If you do that, compilation albums will often be broken into the individual song. Each in their individual artist folder.
Basically if you let iTunes loose on your library, you will entirely lose Finder organisation. Guess what? Then you will be fully dependent on iTunes as no finder based album play system (the excellent Vox for instance) will work well anymore. So there is method to the madness.
Even the songs which don't have correct metatags will all get dumped in a large virtual graveyard instead of being left in their date or album structure.