Nay. I wouldn't even use carbon fiber for my roadie handlebar. Like Raiyn said, I don't like thinking about things on my bike, especially if it breaks I could end up smashing my sternum on my steerer.

I'm not sure about mtb handlebars, but I've heard of certain carbon fiber parts that are nearly bombproof, such as Easton carbon fiber forks (for roadies), but they are few and far in between. The only CF bar I would consider would be one rated for DH/FR, such as the FSA one, but I would still be sketchy.

On the other hand if I was rich and had a lot of time and experience/know-how, I would use CF everything because I can afford to replace them when necessary and can spot damage when it happens.