WebGL is pretty close to prime time as of FF 4 and upcoming webkit based browsers. We have been developing in production mode for it in over 4 months now and are pretty satisfied with the results. AFAIK we have only encountered one crash bug, possibly an ATI driver issue, which was easy to work around once diagnosed. Performance isn't as fast as native but close enough for most applications that aren't bleeding edge (read AAA games).
If you're writing any WebGL code, definitely check out the WebGL Inspector:<p><a href="http://benvanik.github.com/WebGL-Inspector/" rel="nofollow">http://benvanik.github.com/WebGL-Inspector/</a>