I have to start by saying that this site is a fantastic utility, and does a great job of helping me track how I can improve my character and his gear and the like.
My one question--and this may have been covered somewhere else (my searching hasn't been as extensive as it probably could be)--is this: what about reforging?
I don't know anything about Blizzard's API or if reforging information is even available, but I know that gear reforging can make a huge difference in how squishy a tank is, or how much DPS your Warlock can put out.
And while I recognize that a lot of the information about stats tends to be vague, perhaps things like a hit cap check for DPS (expertise for melee), spell hit cap for mut rogues and casters, or other similar things. Because it's so circumstantial, I might not suggest putting weight to it (that's on you guys to decide--e.g. healer priests don't necessarily need hit or even spell hit), but having the information there would be handy.