In almost all my SmartPlaylists I have a condition of:
Last Played - Is Not In The Last - X - Days
Before the 4.5 iPod update, this has worked so that when I listen to a song on my iPod that track gets removed from the playlist for X days.
Now it seems when I add a Grouping condition to my SmartPlaylist it no longer removes that song from my iPod's playlist. (I just tried this with the Playlist Is/Is Not condition and it also does not work)