I haven’t seen one. I’d imagine it’s similar to the “Find my iPad/iPhone” application. You can see the location of your device on a website, people have used it to figure out the location of a stolen device and send the police there to recover it. I used it to find a lost iPad (son left it at friend’s house)…the map did show the location down to the street address, though it was no help at finding it inside the house, that took some old fashioned hunting around and looking between couch cushions. Probably accurate enough for finding an animal more quickly, since you can call the animal once you are in the vicinity ;).
I’d find out what reception is like where you live and where the dog goes, maybe by testing it with a GPS enabled phone or portable GPS device. I know with the GPS in my car (and on the iPad), there are some areas around here without a good line to the satellites (heavy tree cover). Any GPS device has to be able to find three satellites to determine it’s location.