I stay in the saddle a lot more than most of the people I ride with. In general, if I'm out of the saddle it's because
A. The hill is really freakin' steep, and that's the only way I'll keep moving,
B. I'm slacking off and if I stand and pedal slowly(generally 2 gears up) it's probably slower but uses different muscles
C. I'm feeling frisky and trying to hurt someone....which usually is just me.
I find it hard to stay seated at 60rpm, but I can do it standing. When I'm standing I just automatically go 2 gears up. If I go 2 gears up and start stomping in the middle of a long climb it could just be an aspect of the oxygen debt. Having said that, it happens every once in a while.