Saturday (remember how nice the weather was on Saturday?) i went to Angle Lake cyclery in Des Moines (washington) and tried a bike that was called a RANS. It was a big strange looking thing and it had a saddle like you have described Knot. I only rode it for about 1000 feet, and it was fun and seemed to be fairly stable. It was completely different though from anthing i'd ever ridden before.
http://www.ransbikes.com/default.htm
(i rode the Dynamick)