I own a Mac mini with 1500 GB to import all the CDs I have (approx. 3000)
I use MacOS X 10.4.3 and iTunes 6.0.1. with 1900 albums and 25,800 songs at the moment. For that Import I use a cheap external PC-FireWire CD-Drive (48x), to keep the internal drive hale.
The thing is that iTunes becomes more and more slow, when importing. Mainly it takes a lot of time to organize all lists, basically the automatic-playlists, which update automatically. That means, importing itself happens fast. But at start of a track and at the end of that track, it takes approx. 30 seconds each and seems to wait for something.
Please check your settings and try it with a small library first to control everything. I'll not be responsible, if all your lists would be lost or anything else like that. I found the following way by trial and (no) error.
The trick I use, is, to move "iTunes Librarey" and "iTunes Music Library.xml" from "/Music/iTunes/" somewhere else. Restarting iTunes will create new ones. The destination remains the same as before. Now importing goes xtremely fast. After some CDs (maybe hundreds) or when you want to hear from your previous import, export the library and quit. Take the new files named as above anywhere else (trash) and copy your originals back. Restart iTunes and import the "Library.xml" or how you did call it. It takes a while to reorganize. Even the cover artwork will be imported. Check your playlists. Some new ones will have been added like jukebox, radio etc. You can delete them now, or remove the corresponding sections in the newly created iTunes library. Playing, searching, everything does fine, except editing tag information. There I have no idea, but maybe anybody else ...