As part of their progress toward becoming a “world class bicycling city,” Boston has implemented a Stolen Bike Alert program that makes it easy to report a snatched bicycle.
First, you simply register your bike online (it’s free, and you upload a picture). Then, if your ride is stolen, simply report it to their website and they alert the police, local bike shops, hospitals and schools…and everyone who follows them on Twitter and Facebook.  Essentially, you get the cycling community and law enforcement all aware of and looking for your bike.  Sweet.
This represents a killer application of Web 2.0.  It’s free, it’s community based and it’s simple.  Let’s hope more cities adopt a similar system.