I'd say stat tracking like:
-Amount of time spent playing all games total
-Amount of time spent on the forums
-Most played game (Calculated by time spent playing)
-How many unique games you've played (as in how many different games you've played. So playing one game over and over would not add to the stat)
-How many games you've played in each genre
-Favorite genre of game (Based on either the amount of time you've spent one genre or how many unique games you've played in that genre)
A simple way to calculate the amount of time spent playing games would be to just calculate how long the url of the game is open in the browser window. This would easily expoilted but also easily implimented. Same thing with unique games played. Just calculated by the url.
You probably couldn't hand out any sort of points for the stats because they are eaily exploitable. But you could at least keep track of them. Or whereever in the profile the stats would be listed could change color from like black to bronze to silver after so many unique plays etc. Maybe some sort of name given by the stat like gamer newbie, game addict, etc. as you play more games.