The update brings the software from 9.0.3 to 9.1 The changelog is short and sweet. It says:
iTunes 9.1 comes with several new features and improvements, including:
• Sync with iPad to enjoy your favorite music, movies, TV shows, books and more on the go
• Organize and sync books you've downloaded from iBooks on iPad or added to your iTunes library
• Rename, rearrange, or remove Genius Mixes
It's no surprise to see that the bulk of the new features are aimed at the iPad. iTunes will sync with the iPad similar to the way it already does with iPhones and iPods. Hopefully all those purchasing the iPad will take the queue and update before their iPad's arrive.