This is by far the most interesting mix of mobile and GPS that I have seen. The simplicity of drag n drop onto your handset makes it super consumable - as GPS enabled phones become more prevalent, this service should really find itself.
They even have a Zillow Widget for instant home values based on your location. This is huge for investors, home appraisors, and real estate professionals.
The "yeah but" is that this is only enabled for a subset of mobile phones on the Sprint network, and is by no means open to the masses. Same old story there I guess. I am looking forward to a day when you can run these types of apps across handsets... but I won't hold my breath.