Using manual iPod update, Playcount and My Rating (i.e.) will not be synchronized between iPod and iTunes.
To fix this problem, you can use synchronization BUT…
Using synchronization of your entire collection sometimes doesn’t work (because of the limited iPod capacity).
To fix this, you can synchronize a selection of playlists BUT…
Using synchronization (of a selection of playlists) will not allow you to create Smart Playlist for your iPod music in particular.
SmartPlaylists.com delivers clever solution to your burning problems.