I found this yesterday - rottenneighbor.com. I love the concept, but the site is new and in beta - so there's not much content yet. Nonetheless, it's just a great idea for a mashup.

The site merges Google Earth and tags about good or bad neighbors in your area. You can search on locations to see what's up with the neighbors in your prospective new hood.

Love it. I am fine with my present neighbors, but I could have written a book about the axe-wielding homicidal maniac that lived next to me in the loft I bought a couple years ago. Scarrrryyyy!
Link to original post