Down Brick Lane market on a Sunday morning there is literally a fence... a chicken wire one from which stolen bikes are sold. Lord knows what the buyers are thinking, and the police are well aware of what is happening too (but are doing very little about it).
We are now tracking (within the community) where bikes are stolen from, the measures used to protect them and evidence of how they were circumvented as well as where and when the bikes are turning up. With a large enough community (over 12,000 users in the same city) we're able to recover a fair amount of our own property after the event... not to say we're lax about protecting it but that by taking as many precautions and steps that you can you stand some chance of being re-united should the worst happen.
Opportunist crime wherein someone just steals something because it's easy to and then they keep the item now seems rare.
Oh, and if you're interested in bike security these guides on my site are good places to start:
Guide to which locks to use (which are primary security, which should be considered secondary): http://www.londonfgss.com/thread17938.html
Review of a motion alarm: http://www.londonfgss.com/thread24813.html
We also have private areas of the site for tracking stolen bikes, and have worked with companies like Kryptonite to help make their locks better, local police to try and get them to do stuff about the 'fence' and the local cycling associations to try and raise awareness. We're collectively writing guides on bike security too which we hope will be released under creative commons on a wiki and then from there we can encourage bike shops to distribute copies with every new bike sold.
Anyhow... I am more than wandering off the point, which is that most stolen bikes in London are stolen to be sold and that the buyers tend to be regular people who do take them into bike shops after a while, from where some bikes have been recovered. More successfully though, we've recovered bikes from Gumtree and eBay classifieds.
