Bamboo bikes - the verdict?
Strength at high speed? I have ridden my road frame for 2 years now, and have many miles on it. One of my favorite rides takes me to a hilly section where I have a long sweeping downhill. On a good day, I can reach 70 km/hour. At the bottom is a bit of a tight bend where lateral forces are a plenty. The joints and the bamboo are holding up better than I expected. I love it!

Durability in the wet? The natural characteristics of the bamboo are phenomenal, including the water resistance of the exterior skin. As long as you seal it well so moisture cannot get inside (particularly where the skin is not present, like cuts and nicks in the bamboo or where the shoots come out of the sides at the nodes) you have nothing to worry about. I have been caught in some pretty horrendous monsoon downpours here in Thailand.

Weight - My 54cm road frame weighed in at 2.0 kgs. I built it light as I am a 150 lb rider. The last road frame (we call Thai Silk) that went out the door was a 58cm which weighed in at 5.4 kgs. 

Joints - The only place you really need steel is where the bearings or threads go, like head tube, bottom bracket, drop outs (even then, there are ways around this as well). The joints are plenty strong from carbon fiber or fiberglass. Thermal expansion factors are something we consider on our proprietary joint construction. Some builders have abandoned carbon fiber because it is too stable, others have abandoned hemp/sisal joints because the rigidity degrades too rapidly. If you choose to use steel joint lugs, you will need to overcome the challenge of a good bond between the bamboo and the steel. 
Take a look at our site if interested BambooBikeMaker.com or email me at philwebb333 [at] gmail [dot] com