I was thinking today about how hard it is to get playtesters for games. It gave me the idea for a feature called "Game Exchange" where two developers would be paired off at random. Each developer could play the other's game and leave a comment and review on it.
It seems like it would be a good way to get playtest feedback on games that are early in development. It would probably also be a fun way to discover new games.
EDIT: I actually just thought an easy way to do this without any complicated feature development would just be to make a section in the forums for it.