A good friend has made a couple of bamboo MTBs - using carbon fibre to bonding the individual bamboo 'tubes' together. One of the frames was a full-susser (incorporating an old alu rear swingarm) and survived a gruelling 24hr race.
If you've got the time and effort then you could build up a great and utterly unique frame!
To say nothing of skills and facilities! I'm currently knocking up some poor woodwork, it's getting there, I've put in loads of time and effort, I'm pretty skilled at mechanical things but my facilities are a workmate in a back yard, it's proving to be bloody hard work.
Well, they certainly appeal to me. A bike has to look good, made good - it could never be just for riding, pride of ownership (not necessarily snobbery) I just love spending money on good kit - but you buy it to use, not just look at - it 'ain't a painting. Obviously I see the point about taking it out in the rain...I can't bear to get my new Brooks wet...and you can see why people leave rusty clunkers locked up at the railway station, so they're not bothered whether it gets stolen or damaged.