I recently tried a Sella SMP Composite which I liked pretty well but had a few complaints with. Although mostly I just wanted a project. Here's the original saddle:http://www.smpselle.com/smp4bike/images/stories/demo//composit/01.jpg
And here's mine, which still needs some final sanding and clearcoat:http://people.freebsd.org/~jeff/bikes/saddle8.jpg
I have a spray gun on order to apply clear but I also ordered some kangaroo leather and may wrap this one. The goal wasn't light weight but it is presently 92g. This is lighter than the full carbon sella smp! The shape changes include a shorter and slimmer nose, a wider center channel, and a filled in back. I don't put my bits on the nose or very back of the saddle and filling it in made a simpler shape to mold with better mechanical properties. The sella design results in an overly stiff and unforgiving saddle when fabricated out of carbon.
I took some pictures of the process. Here's the mold I took off of the smp and a plaster copy:http://people.freebsd.org/~jeff/bikes/saddle1.jpg
The first mold I made before changing the shape further:http://people.freebsd.org/~jeff/bikes/saddle2.jpg
The first test shell of the right shape. It's only two layers of carbon to experiment:http://people.freebsd.org/~jeff/bikes/saddle4.jpg
I ended up trying 2, 3 and 4 layers. I stuck with 3. It's all 3k weave as that's what the supply store had. The final shell was 30g after being cut to size. Here it is as it came out of the mold:http://people.freebsd.org/~jeff/bikes/saddle6.jpg
I weigh the epoxy and lay it up only slightly too wet and then vacuum bag it. At 3 layers it had a comfortable and slight springiness to it. The rails added some excessive stiffness. Here's how I bonded the back of the rails:http://people.freebsd.org/~jeff/bikes/saddle7.jpg
And one more bike shot:http://people.freebsd.org/~jeff/bikes/saddle9.jpg
There are cosmetic defects but I consider this a prototype. it is very strong. I have ridden it over the local 'cobblestones' and purposefully jumped up and down on it as hard as I could stand. I am currently making carbon fiber rails. I will probably cover this one and make another with an improved surface finish now that I have learned better techniques. I also ordered some nicer fabrics online. I suspect with carbon rails it will only be ~70g.
I have to thank carbonfiberone from weightweenies who gave me a lot of advice through this project and has gotten me addicted to epoxy fumes.