I like a few covers but generally speaking too many cover versions add nothing when compared to the original and look like nothing more than a cheap cash-in. Something like 30 Seconds To Mars covering Stronger is an example of what I'd call a good cover - it does it differently and makes it their own. Something like The Foo Fighters covering Baker Street - it's very well done, as you might expect but it's not distinctive enough to make me think it was worth doing. And then there's abominations such as Jedward covering Teenage Kicks - what made them think they could ever do justice to such a song is beyond me, there's a special circle of Hell reserved for that sort of thing.