Thought about it. The actual build process (laying up) isn't really that hard, but designing the frame (and deciding where to put what type of carbon cloth, and in what direction) and making a foam core or mould are very difficult and time-consuming. Also, you'll have no precident for how strong it will be (whereas a steel builder will now that, as long as his or her brazing is up to scratch, the lugs and tubes will make a good bike), so some form of testing will need to be undertaken (possibly a destructive test, like the guy on Sheldon's site). And bare in mind that it's gonna cost a bit too, for what Sheldon's pal spent you could have a top-spec 'normal' bike (about $2000 I think).
But if you're willing and able to spend a lot of time and money making things like moulds and jigs, that you'll probably only use once or twice and no-one will ever fully appriciate, the possibilities are endless. Just think how many weird and wonderful carbon frames there are out there, from crazy monocoques like the Lotus Sport bike, to bonded tubular ones like the Colnago C50, to the step-through that Sheldon's guy made. Just keep an open mind about design, and you could end up with a bike unlike any other.