KTOMG is super awesome!
The only thing missing is the ability to let your buddies add you as a 'friend'. If you add a friend, you could let then set permissions on a List to allow friends to collaborate and add games :D
You could then see which friends have played the games in your various lists and or friends lists.
Basically, if we can invite friends to the site, we probably want to follow each other and follow each others lists to some extent (assuming the permissions are set appropriately)

Our use case is as follows:
There's a group of us that do Game of the Year videos and we want to keep up-to-date with what we think are contenders. You could then see who has played the game or completed the games. From there we would start discussions or at the very least 'rate' a game on a 1-5 star basis.