AMD has officially conformed this see:
http://www.linux.com/feature/119049
It appears that the first version of the open source driver will be released in about a week but will be 2D only at that point. I would expect it to be 3 to 6 months before the open driver has OK 3D.
It appears that the most recent closed driver from AMD is a big improvement over older versions as well. So on every front this is good news for X11 users.