iTunes Home Sharing never updates Play Counts or Ratings from iPhone
This has always worked for me and here is a test I just performed on iOS 5.0.1 (9A405) and iTunes 10.5 (141).


make a smart playlist of songs rated higher than three stars and browse it on your iOS device
the only bug I see is sometimes when you go to settings, the current stars don't show, but when I change the rating it is reflected in the iTunes listing almost instantly (the change pushes over WiFi back to the iTunes and causes the display to refresh after each change).
play counts get updated at the end of the song, last played is updated correctly.


If this doesn't work for you, you may have to isolate the error in your setup. I would start with a new user account and moving 5 songs to a clean iTunes library. Be sure you quit iTunes on the "main" account if you use fast user switching - home sharing might not handle two copies of iTunes running on the same computer well. Another quick check might be to disable any firewall software on your mac. Something is off on your setup and without more testing, it's hard to guess exactly what.