I designed and built a fixed gear track bike using oversized carbon tubing. The seat, drop outs, BB and head tube contain no metal at all, this frame is 100% from low density materials. The frame was very quick and easy to fabricate and ended up being quite light and extremely stiff. The project has a website at www.ideas2cycles.com for more details about the design and manufacturing process.
The headset is semi-integrated and the bottom bracket is a press-fit model. The wheels are old tubulars I had laying around and converted to a 120 mm rear spacing with a welded free hub body. An old Selle Italia Flite was used as a model for a silicone mould that was used to lay up the carbon seat. The seat shell was then bonded directly to the 50 mm (2") seat tube.