iTunes 10.2 just snuck in a very cool feature for Home Sharing—which iOS 4.3 devices now support. If you go into preferences, you can check the box that says "Home Sharing computers and devices update play counts," which means that when you stream music to your other computers, Apple TV, or iOS devices, the play counts in the iTunes that you're streaming from will go up by one. As if you were listening to the song on your actual iTunes or iPod.
It's a very cool feature for people who rely on play counts to generate smart playlists of songs they've listened to a bunch of times, or not recently, or any other cool thing you can make by knowing how often you've listened to a song.
I've been waiting for this feature since iTunes had the ability to share your library to other computers on the same network—which is to say, forever. Though, I just tried playing back a few songs via Home Sharing on an iPad, and the numbers are not increasing. Perhaps I'm doing it wrong?