Great app, big fan.
I put up a feature request way back, for the video history and it got accepted. Hope this one makes sense also.
For the people who use playlists and watch multiple playlists at the same time, it would be usefull to mark a playlist item as "watched" once you have finished the playback on the full video. This helps you remember where you need to resume the playlist from.
I would imagine this is not a really big task, hope to get some feedback from you guys.