With the chain detached, when I spin my rear wheel it slows down really quickly (2 turns?) as if the brakes are lightly on. The brakes are well clear of the wheel though. Any idea what it might be? The bike is about 2 years old and I have not done any maintenance to the bearings, so I'm wondering if that might be it. But I have no idea if those are really the symptoms.
I've had a similar thing happen on an old fixie of mine. It ended up being that the rear axle was every so slightly bent, and that was causing huge amounts of friction. You can try oiling up the bearings. If that fixes the problem, terrific; if not, then you might need to take the rear hub to get looked at more thoroughly. Good luck.