The one thing I really like about them is that it often gets me to fully complete a game I wouldn't normally do everything in. Most games don't give you all the points just for beating the main storyline, so it encourages you to do all the extra side-quests or whatever.
I dont see the big fuss about gamerpoints, it means nothing. I have played people with little points who are absolutly amazing, then people with loads who are pants. If there was a reward for them such as for every 1000 points microsoft give you 100 market place points that would be worth getting them.
And then there's the people who only care about their score, which, of course, is dumb.