Play media from any iDevice
Prior to iTunes 10, it was not possible to play contents of an iDevice in your computer without syncing the device to iTunes, thus losing what songs were present in that device. But that limitation has been removed in iTunes 10. With iTunes 10, your friend can plug in his iPhone into your PC and listen to his music and podcasts, watch his TV shows and movies, and all this without having to turn off automatic syncing.
Get back the horizontal control buttons (Mac only)
Almost all Mac users are used to the familiar horizontal traffic light control buttons in iTunes, but the new iTunes has set them in a vertical fashion. This may not go well with many of the loyal iTunes fans, as this would go against the UI guidelines set by Apple themselves. But there is a way to revert back to the old horizontal system. All you need to do is simply run the following command in Terminal, accessible through Applications > Utilities.
defaults write com.apple.iTunes full-window -1
Restart iTunes, and it's fixed.
Select your top 10 songs (in Ping)
By default in iTunes 10, Ping automatically populates the top 10 songs and this is actually decided by the purchases you make, rather than the songs that you actually like and listen to often. You can fix this problem by going to My Profile > Edit profile, scroll down to Music I like. Here, check Manually pick the Music to Display. You can use the Search for Music dialog box below to search for songs you actually like and want to be included in the top 10 list. Currently, you can choose only songs available in iTunes, hence quite a few of your local favorite songs cannot be listed.