Tim has one (as already mentioned upthread). We took one for a test ride a few weeks ago as a potential niche filler of a seperable tandem*. It's a nice bike and rides well, but we came to the conclusion that we didn't need to spec up a bike to £4.5k to fill such a niche (but if someone spots one second hand please point me in the direction).
In terms of suspension on recumbents I have both a suspended SMGT and an unsuspended windcheetah. For comfort the SMGT wins hands down, and a lot of non-fast recumbents (when luggage and comfort is a requirement over speed) are at least partially suspended, even some quick ones are at least partially suspended. The problem is you can't take the bumps through your legs as you would on an upright. I suspect that you would otherwise have to run a low pressure fat tyre for the benefit of the stoker which would lead to a danger of pinch punctures.
If you want to try one with suspension chat to JD cycles - their demonstrator is equipped with one and they'll happily let you play.
*We have since noticed that Virgin Atlantic's cycle policy stretches to taking tandems free of charge as sporting goods.