Among the bugs that have been fixed in the first Mesa 9.2 stable point release include memory errors in Mesa spotted by Valgrind, Unigine crashes, some Piglit issues, and other changes.
The brief Mesa 9.2.1 release announcement can be found on the Mesa mailing list. Some of the Mesa 9.2.1 changes can be found via the Git news item. There's also the Mesa 9.1.7 changes.
Meanwhile, development on the next Mesa release is in full swing and will likely be known as Mesa 10.0 with a release target of November. There's improved OpenGL support, performance improvements, better hardware enablement, and numerous other changes, which have been covered in numerous Phoronix articles already and will continue to be covered as development happens in Git.