Version 8.1 is said to have significant speed improvements for dealing with large libraries, and also a faster iTunes Store and zippier syncing of devices. Yay!
The Genius sidebar now includes suggestions for movies and TV shows, and the new version will also allow you to import your CD's as 256 kbps iTunes Plus format.
That all adds up to a nice update. So keep your eye on 'software update' under your Apple menu, or ask iTunes to 'check for updates'.