I love them. When I beat a game, I always tell myself I'll go back and get any miss on a second playthrough, which rarely ever actually happens, so I'm no completionist.
I do have the mark of shame that is Avatar on my gamercard though, and I spent a bunch of free time one summer trying to keep up with or surpass a co-worker of mine. I did a bunch of games offline so he couldn't see my progress, surpassed his score, then my memory unit got fried and I lost a shitload of points. :'(