If you're going to stand, be sure to shift to a harder gear first. That way, if you must sit again, you can shift back to an easier gear and not suffer so much.

When you are seated, be sure to push your butt way back in the saddle & pedal with those glute (butt) muscles. It will save your knees & your glutes are stronger than your quads (top of thigh) or hamstrings (underneath part of thigh..think "cellulite" )

I'm with the "spin" crowd. You may not hurt your knees today or tomorrow, but grinding it out will eventually take its toll. If you're a "seasoned" rider like me, you want to be careful of your joints. Additionally, you don't want to build bad muscle memory. Get used to spinning up hills (and into the wind).

Oh, and I ride a double too.