I broke a seat post bolt in Hawaii when we were touring on our tandem. Overtightened it and snapped it off. We were in the middle of nowhere, so we swapped out Thom's seat post bolt and relied on my handlebars to keep his seat in position. It was our first day of touring too. Not an auspicious beginning.
Anyway...
For suspension, I have a Thudbuster on the tandem. I've been pretty happy with it.
V.