Lets say you're planning to move to a new neighborhood and want to know about the bad neighbors before you commit to renting or buying that house. Or you already live in a neighborhood and want to know about the "bad seeds" nearby. There are two different maps mashups that give you the tools to do just that type of neighborhood reconnaissance.
The first one is RottenNeighbor.com. This one has a database of "bad" neighbors as submitted by others on the net. What types of bad neighbors are being reported here? Noisy, mean, destructful, you name it it's there. I see this site as being a lawyer magnet at some point though as I'm sure there are some inaccurate reports on there by some who might be trying to get back at said neighbor and probably some silly whining as well. Still, it's interesting at the very least and hey, it might save you from moving into a bad situation. To use it, you just type in the zip code you want to search and it pulls up a Google Maps with markers showing various "bad neighbors" along with a listing of those bad neighbors below the map. Here's a screenshot for you:
Rotten Neighbors even has a weblog with "helpful" hints on how to tell if you have a bad neighbor and what to do about it. It has an easy link "contribute to this map" so you can put in your list of "bad neighbors."
The second mashup is a Windows Live Maps Mashup that takes the registered sex offenders database and shows you where those registered sex offenders live. If you have kids, this is very good information to know about a neighborhood.
I wrote about this one last month and it is a heavily viewed site. To use it you just input the address, city or zip code and it instantly shows you a list of names of registered sex offenders with a map of their registered location/s pinned on the map. It even shows the crimes and a mug shot of each offender.