The plan has been for 1.9 to be a stable series for a
long (at least over a year) time now. I'm not sure there are any concrete plans for 2.0 at this time. If you use Ruby, now would be a good time to start getting comfortable with 1.9, though there doesn't seem to be much rush.
I updated one of my projects to work with 1.8.6 and 1.9 a couple months ago and it was mostly painless. I'm looking forward to the nice performance improvement and some of the api changes when it becomes production ready.