It only took 11 months, and 77 games (!!) but I have past 10,000 Gamerscore Points. Now, I am not the Gamerscore whore like Matt (he is close to 30K right now), but 10K is a milestone.
Does the Gamerscore work? Yes, it does, I don't think there is any question about that. Achievements give you more reasons to play your games. Beyond artificially lengthening the game, it really squeezes more out of your $60 purchase. That is a very good thing.