Those of you involved with the TA thread in the 360 forum will know I'm a sucker for gameplay stats and I recently stumbled across Raptr. It doesn't aggregate score like the 360s True Achievments, but it DOES combine your gaming data from XBL, Steam and PSN.
I must say I signed up for it yesterday and I'm loving it. The desktop app is incredibley nifty and although the Steam cheevos can be a bit ropey (it won't actually add your stuff unless you launch a game with the desktop app running), I'm impressed with it's detail so far. The forums are pretty rudimentary but there seems to be a nice little community going and the way you automatically 'Follow' games you own means some nice stuff comes up in your news feed.
I just wanted to throw it out there and couldn;t find a thread. Anyone using the service feel free to add me - Abueloshika