I just snagged a Kryptonite NY lock (with a large cage). IT IS HEAVY.

I think it would take a lot more leverage than a seatpost to bend it. Perhaps it would help deter thieves from making the attempt.

I lock my bike a lot, but there are some places where I won't do it. So, I park it at stores, but won't park it at a bus stop (no subway lines around here).