For a while I've been looking for an addon that would track drop rates. There are two different approaches that I'd like to see. One is to track the drop rate for a given item (mobs/nodes that drop: %) and second is to track professional nodes like herbalism: what you got when you herbed i.g. felweed: how often you got a fel lotus / mote of life / fel blossom and on average how many felweeds you've picked on one node. Or for example how often you got a thick clefthoof hide when you skinned a clefthoof bull.
For the professional one, I've only managed to find a very old addon that tracked stuff for skinners. I've had to dig it up several times and was too lazy to bookmark it on Curse (fr), so now I can't find it but it really had a nice interface. Also an addon that tracks profession stuff like that doesn't sound too hard to find but I still haven't managed to find one, at least one that wouldn't have been abandoned on beta stage over a year ago.
The first one sounds like something that would possibly be difficult to construct, but I don't really know for sure. (also I guess it would be sensible to have some kind of a white list for items to track since there aren't that many items you usually can farm, mainly motes & rep items)
edit: http://wowui.worldofwar.net/?p=mod&m=579 was one that I found but surprisingly enough, it doesn't work. Tooltips are nice though I'd like to see a nice frame for profession stuff (so that I'd see what that Copper Vein gave me even if I was in Ironforge).