I love the achievements on giantbomb! I use this site over the WoW Armory for seeing how my progression. However i would like to sort the achievements per game, so i can hunt down the most rare ones. Also i would like to see a feature displaying the number of people who got it in the achievement itself, rather then having to click on it.
I think the functionality is great as is, but i expect GB to make more of a community feature of it.