We've heard about cases where people commit a crime and post (or should I say: boast?) evidence of it at MySpace. Police cruise the Myspace site, find the evidence, and make an arrest.
Closer to home, Princeton University Security people made an arrest last year, based on evidence in a Facebook photo. There was a big upcry. Students seemed to feel that what they posted in Facebook should selectively be regarded as private (by their enemies, not their friends). Now it's occurred to me that local governments can peruse other web sites to make arrests. In fact, I predict a pretty high return on effort.
I've noticed that when you display a map at Google Maps, the map will show businesses close to your center of attention. Maps of areas zoned for homes are even likely to display businesses - operated out of homes - that have no zoning variance to permit their operation. Municipalities, make that bust! It's as simple as that. (And yes, I'm thinking about concrete examples.)