Well, I've never sat on one, but Bicycling (which is a lousy magazine, I know) did a carbon saddles roundup a few months back and came up with some helpful conclusions.
They evaluated the Selle Italia, the Selle S.M. Carbon Aspide, and the Apollo. The Selle Italia, they reported, was extremely similar in feel to the SLR, and would be an easy choice for anyone who uses and prefers that saddle. The Aspide was doing alright until it cracked after the rider hit a moderate bump -- they concluded there might be some durablility issues.
The Apollo, which is actually priced really well in comparison, was the hands down favorite. The custom fit leant serious comfort, and it was rock solid -- they put miles and miles of both road and rough XC trails on it without incident.