This is the first time anyone has brought it up. I think its a great idea and we are working on it. For now you can try this
http://identify.whatbird.com/iphone/
I'd like to hear your thoughts. It is very basic but we are thinking about expanding it to allow the same features that are on the Firefox toolbar we just released (3 filters - location, shape and color).
Mitch
iBird Explorer: Finally a field guide as light as a feather. See it at http://www.ibird.com