I'm looking to do a little pc gaming after being out for a few years, I have the sense now that buying a used game is risky because they need a key to activate and the first user will have already used it up. (I'm talking legitimate product like half.com or amazon partners, not craiglist wares or whatever). Can anyone clue me in to the new rules? Is it just a concern for multiplayer online games, or is it all games e.g. - what about a game like civ IV where I would likely only ever be single player?