The Canary build goes out automatically without being looked at by a human, so there's a very real possibility that it will be unstable. Currently there's some strange crasher in the PDF viewer, for example.

You can install Canary "side-by-side" with another channel, so you can switch back to something more stable if canary goes pear-shaped.

I've been using it daily on OS X for about 2 weeks. I haven't had any crashes or unusual problems.