Very interesting. I would love to see someone build something similar for other cities, perhaps overlaid with Points of Interest and mass transit lines. I think it could be made to be useful for tourists and people who are new to an area.
However even if it can't be made into a usable product it'd be very interesting to see.
I used to have markers representing high-rated yelp locations on PadMapper, but they weren't too happy about having their data cached (which is necessary in order to make it smooth), so now it has to be pulled manually by the user.
Transit lines are something that should go on PadMapper at some point. I hope Google opens up their transit layer sooner rather than later.
However even if it can't be made into a usable product it'd be very interesting to see.