skeletonbow: Collector mentality is part of it. Steam rolled this out because it is all a part of the psychology of addiction and marketing. It isn't necessarily all a bad thing if someone enjoys it or perceives benefit from it of course, but all of that stuff is totally lost on me. I've got a bunch of trading cards and other crap in my Steam account that will more or less sit there and rot. I couldn't be bothered to bring the page up let alone trade or sell the things. Putting an hourly price on my spare time, even if I sold them at twice the going rate my life would only be shorter for the time spent. ;o) That's not to say that I don't collect anything myself, but I'm kind of indifferent towards such things for the most part, and totally don't care about it for games.
I think I'd be fine with the whole trading card mumbo jumbo, and to each his own, and yadda yadda, if it wasn't for the huge cut Valve takes from the benefits of trading. I'm not into trading virtual stuff, I can find game art on Google for all I care, but I'm O.K. with others being interested, and would be willing to trade them any card I earn. But I'm not O.K. with throwing unearned money in Valve's pockets. You want my money? Fine, then give me good games at reasonable prices, but don't just wait for Joe McCollector to pay half a buck for my "Bastion generic art #2" card and take ten cents for it (not sure on the actual percentage, don't care enough to check) without it actually taking any effort for you or you providing any service whatsoever. So yeah, my cards will rot as well, I guess.