Dive in, the water's fine! You may experience a few bumps along the way, but there are a lot of people already in the water ready to help you out. There are already production apps running Rails 3--just don't use it for anything mission critical.

I think that was what the parent's question was: when will it be ready for "anything mission critical"?

I've heard they're targeting RailsConf - but it's really anyone's guess. The frequency of commits doesn't seem to be decreasing.