As I said, US players aren't really working at this point, and the site blames the Armory's instability (one more reason for Blizzard to start breaking out the stats). But I looked up an EU player I know (as you can see above), and the app is pretty cool -- it'll tell you where you're missing sockets, where your gear could be better, what your talents are "meant for," and where to run instances so you can get better gear. Pretty neat.
Now, a disclaimer: you should always spec and gear how you like, not how some online application tells you to. But everyone should be interested in making their character better, and a setup like this could be very helpful in figuring out how to get where you want to be going. Hopefully the site's creator (early apologies for sending traffic to the site, but it'll die down after a while) will figure out how to work with the Armory, or Blizzard will get it into their heads that opening up Armory info in XML or other open formats will make this easier for everyone.
[Via AA in its slick new location]