I've thought about it a couple of times - building a brakeless freewheeled bike and then chasing them down once they get on it. It's all fine and dandy to say that bike thieves deserve to die but i don't think that any of us really mean it and would feel like **** (not to mention probably face criminal charges if it was proved that we intentionally set up the trap) if someone got seriously hurt and/or killed.

A light beating, however, wouldn't be bad. It might send the message to other bike thieves that they are going to get ****ed up if they mess with people's bikes - on the other hand, it might just prompt them to start carrying bigger knives.