I've been using the 3-branch for a while now, on both testing as production sites. It's stable enough for me to work, and I haven't run into any issues.
It's been said that one of the main reasons that Elllislab never released CI3 is because of the lacking documentation. Of course there have been individuals publishing the docs anyway, but I think it's worth noting that BCIT has now published them on codeigniter.com too.
It's a small step for documentation, but a giant leap for CI!
