Joel Burlslem stumbled upon a possible iPhone-based interface for Zillow. His post update reports that it may have been subject of a takedown order from Zillow, as it was developed by a third-party.

My clientele are certainly tech-savvy, and while I might have some fun playing with a feature like this, I just don't see a huge need for such immediacy in having to ascertain a property value on the fly...unless you're one who likes to draw up offers at the curb of the property you're wanting to buy.