The idea that there are 1000's of professional bike thieves looking for bikes in your area is just silly. 99% of the bikes that get stolen out there are stolen for 2 major reaosns. Either the person didn't lock it and the bike thief just HAPPENED to be there at the right time. Option number 2 is the lock was a cheap chain lock that just required daddy's bolt cutters to get past the thief in question probally knew where the bike was kept most of the day had seen the lock, and realized how easy it would be to bypass. Ran home got the bolt cutters and returned for the bike.

With that said a good lock makes a diffrence. In most cases thieves won't have access to the type of tools needed to take a bike on the fly like this. Secondly if the choice comes down to grabbing the bike next to yours using the cheap chain lock, or going to find the tools to come back and attempt to get your bike with the better lock i garantee you you will not be the one walking home that day. Theives by nature are lazy people who will almost all ways go for the easy grab.