The launch of iTunes 10 in September left a lot users disappointed for several reasons. In addition to the lack of a complete rewrite that many people were hoping for, the highly underwhelming Ping social network was added, and the subsequent 10.0.1 update replaced the former Genius sidebar content with Ping.
Thankfully, despite Apple's insistence on tightly controlling the user experience (which is generally a good thing), the company has been willing to reverse course from time to time to restore functionality or designs that users preferred. Users that miss the Genius sidebar content will be happy to learn that Apple has made server-side changes to iTunes (meaning no software update is required on your end) so that we now have Genius recommendations back in the iTunes sidebar.
The sidebar now combines the functionality of the Genius and Ping. Genius recommendations are always available, and if you use Ping your activity is also displayed. Recommendations now appear as soon as a song is selected, before it's even played. It's a step in the right direction; hopefully next year we'll finally get the ground up re-write that iTunes so desperately needs.