We've been standing regularly since we first got the tandem. We had to work through some issues - but we have settled in on how we go about it. I simply say up - my stoker goes up and I follow on my next pedal stroke. This works extremely well for us as I can feel when my stoker is up and allows me to use my pedal stroke I want to lead with. We are not comfortable with one or the other standing solo.
We usually stand to power up some short steep rollers or when it's a long climb or a very steep climb. This was shot during Cycle Oregon in 07 going over the Cascades on a 50 mile - 6,000 foot day. This was the second to two - 2 mile sections of 8-10% grade. Needless to say - it was tough.