none here, I've never had a bicycle stolen in over 40 years of being an adult riding a bike. but i do have insurance, if a bike gets stolen and it's worth quite a bit more than $500 i call my homeowners insurance agent. When you consider that the cost of these GPS systems start at $160 plus $5 a month, it won't take long (about 4 years) for the cost of the system and monthly payment to exceed your insurance deductible. In addition to that the GPS system for some reason that are in these bike things are only accurate to about 500 to 700 feet, which in a dense building city may still make it impossible to find your bike, or if the bike is taken inside a building all tracking stops. In addition with a healthy fully charged battery you only have 7 to 13 days to find the bike, that seems like a lot of time but if the bike is in a dense area may not be enough time, or what if you hadn't recharged it in a week, then you may only have 1 to 5 days to find the bike. And if that wasn't enough, the range from your mobile device to the bike being tracked is less than a mile and half.
Sure 20/20 did a report about these units and tried to bust bike thieves, but 20/20 news crew and a cop were in a van waiting for a thief to steal the bike they rigged and watching, and they had to hustle to keep the bike within range of the Iphone they were using or else they would lose contact and lose the bike. So now you're inside a restaurant, a thief cuts your lock and goes, you get notification of the event and go outside to chase the punk, but he's pedalling away at 20 or so mph and you're on foot, so you start running but soon the bike and the punk are outside of your 1 1/2 mile range and you lost your bike. The punk then puts the bike into a vehicle and takes off and is even further away with no idea which way the punk went the bike is now gone forever...unless you get very lucky and find it on Craigs list.
I just don't see the point in these things yet, maybe someday if they get to the point of having infinite distance from your phone then maybe there's a point to having one. Problem with that is that before that day even approaches thieves will know about this technology and start looking in the places where the technology is hidden, pull it out and toss it in the trash, so now you track it and find a dumpster instead of a bike...but hey, at least you get back your sending unit which you can now put it into a new bike without having to buy a new GPS unit.