Everyday, when checking the Portal I keep on seeing Portal Defenders and Thing thing arena 3 at the top of the portal, and we all know why they're there: because of the achievements (and the awesome gameplay). I have this urge of achievements that makes me wanna play this games, at first an achievement like 'jump once' will get 5 medal points, then you'll keep coming for more... it's a waste of time, and what's the purpose of having those medals? so your anti-social friends can see them and will say something like 'OMG that's so awesome, I think I have a boner :o', well guess what, they don't care about your achievements because they're doing the same thing, wasting hours in the computer.
so remember kids, play casual.