I think many people are riding in too high a gear. I know its macho and signals how strong you think you are, but climbing in high gears requires a lot of power; if you dont have that power, the hill will call your bluff. You need to pick a gear which you can climb with a good cadence, at YOUR power, not that of Lance or some other elite rider.
I use a 28-28 for the steepest (25%) hills.