I have more than one bike (yes, I'm one of those dorks) and I would be fairly upset if one of them were stolen. But I also have their serial numbers logged at home, in a safe place, so that I could report that to the police if one were stolen and I'm certain that after doing so... nothing would happen. I'm guessing that if you see your bike get stolen and can somehow stop the thief that having this proof is useful to the police (who can hand it over to you). But 5 minutes later, once that bike is going... I'm guessing the police can do nothing.
So this helps by targeting the buyers? How many stolen bikes are really stolen to bike shops? I would think that a junkie wandering in trying to sell a carbon wunderbike is going to have much luck. And if it's targeting the end consumer... well, I would probably check this registry, but I'm pretty certain that a dozen other people won't.