A lefty fork??

Went a a LBS up near my sister's this week and saw something very interesting...2 Cannondale bikes with a "lefty" fork. I think it was the Rush and the Rize.
It was actually a bit strange looking.:?

Just wondering if any one knows anything about these bikes..performance, quality of the suspension, why the "lefty" shock, the advantage, etc?
Just really curious as I have not ever seen anything like it.