Here's a failure for everyone to chew on:

Yesterday while putzing along ~ 16 MPH on a residential street the captain's seatpost on the Speedster failed, leaving beloved stoker holding a useless stoker handlebar while I'll had to pull myself forward to get my hands on the brakes (good thing I had both hands on the bar). Stoker was super-smooth at keeping her balance, we got the bike stopped safely.

Specifics: Post is a Zoom aluminum post (no longer in biz, AFAIK). Failure was at the point where the post enters the frame (a natural stress concentrator). Approximately a 3/4" long fatigue crack at the front of the post, the remainder of the post cross-section failed in brittle fracture (textbook failure for aluminum). Post is 13 years old, has about 25,000 miles on it. It would have received a cursory visual check sometime in the last year.

I got Mel @ Tandems East on the phone to run through options for replacement posts. I need a setback post to get my position right, so a Thomson is off the table.

Mel had a couple of Ritchey's on the shelf which I pulled the trigger on.