It can be a problem anywhere, but mostly focused on bikes that are easy to strip/sell and common enough that they don't stand out. That means sportbikes and generic cruisers here in the states. A friend of mine had a CBR600F4 locked/covered in his parking lot (suburban CT) and some guys came by one night, clipped the lock and lifted the bike into a truck - right outside his window.
Around me, bikejacking had been a big problem for a while, though seems to have slowed down recently.
Making your bike more difficult and less desirable to take than the one next to it is the best defense. Keep it covered, use multiple locks, with one preferably attached to something solid, and leave it somewhere lit and passed regularly.
Also, a mass of bikes usually means a mass of bikers, and for some reason we still have a reputation of being mean SOBs. Thieves, therefor a less likely to go after bikes in a group.
Of course, there's no stopping someone who is motivated enough. Best you can do is make it harder.