Apple has released iTunes 9.2 with support for iOS 4 and iPhone 4, along with a few other minor changes.
On the iOS front, iTunes 9.2 adds support for syncing the iPhone 4, syncing and reading ebooks with the iPhone and iPod touch once they've been updated to iOS 4 and iBooks 1.1, organizing and syncing PDF files as books with iBooks 1.1, organizing apps into folders on the Apps tab, and faster backup when syncing with iOS 4.
Nonetheless, Apple has made at least one other change to iTunes, an improvement that enables album artwork to appear more quickly. You might also see comments about fixes for security vulnerabilities related to ColorSync profiles, TIFF files, and WebKit. The good news? Those security vulnerabilities and their associated fixes, according to Apple's security notes, affect only the Windows version of iTunes. If you notice any other changes, let us know in the comments!
iTunes 9.2 is a 101.99 MB download from the Apple Support Downloads site; it's also available via Software Update. When you install, expect it to upgrade your iTunes library and album artwork thumbnails.