The site boast to be the "one stop shop" for all of XBox 360's gaming achievements. Sounds nice. But the site is not much right now. So far it just lists the achievements and the associated Gamerscore, plus it has the achievement icons for your viewing pleasure. The site forums seem more useful then the site itself at this point, but I would keep a watch nonetheless.
Whoever decided to add Achievements to Xbox 360 games is a genius. They add even more replay value. It was just a matter of time before a site like this popped up. Although I am sure GameFAQs will have Achievement FAQs up shortly, unless they already do.