Isn't PadMapper just a ripoff of
http://www.housingmaps.com/, which was the first of its kind?
I developed http://www.cribq.com because at the time, both PadMapper (if it existed, can't remember - according to domain records padmapper.com was registered after CribQ launched) and HousingMaps were too simplistic and behind on listings to use. HousingMaps had no organizational tools - so I suppose PadMapper "ripped" that idea off of me? (CribQ website is not actively developed anymore, but the iPhone app is quite popular.)
Seriously, why does this accusation come up every time someone launches a site with housing listings on a map? Even if the site is similar, there is no shame in "ripping off" ideas - you will always do something different and hopefully better or useful in some way. If you manage to copy an idea and survive, you've either done a better job marketing or a better job building a product for some segment. Either way, we all win.
Developing a site that is an improvement, different take, or even a copy of another is not a ripoff. Is AirBNB a ripoff of VRBO? Is Google a ripoff of AltaVista? Is Gmail a ripoff of HotMail? Is TechStars a ripoff of YC? Facebook a ripoff of Friendster? You may not agree with their tactics in some cases, but generally the founders/creators have a vision that differs from the site they "ripped off" and have a reason for creating their own version. And would somebody PLEASE rip off Craigslist and win?
Copy away. Or as Steve Jobs says, "good artists copy, great artists steal."