I have two B800s, one black, one yellow. The black has been back twice for a cracked umbrella mount, they told me there was a batch of bad black housings around the time I got my first one, and the second one. The yellow has had no problems.
As for power, th 800s are a good compromise. I would not go with the 400s, just too little bang for your buck.
All ALien Bees are fan cooled, have stepless power adjustment, and are small and light. I have two B800s and reflectors, as well as all cables in a Pelican 1550 case and it makes them real easy to carry, while protecting them from anythign but fire.
The product is not the best in the world, but at that price point there is nothign better. And the company is a joy to talk with. I have actually received personal emails from Paul Buff, the owner of the company, on a SUNDAY. He was checking the email on his day off and helped me get the first light replaced. That impressed me...