I whole-heartedly agree with Whipple that that Xbox Live Achievement are underdeveloped and should have some tangible use.
Whipple proposes the gamers could spend their Gamerscore points on downloadable content (possibly content designed specifically for Gamerscore purchases). That's a good idea, as long as one's public score continues to represent all of the player's Achievements while the spendable points from those Achievements is presented elsewhere.
Another possibility is for Gamescore to unlock privileges. The higher the score, the more privileges. This rewards people for playing games.