Mesa 11.1.2 brings fixes "all over the place" from core Mesa to all of the common Mesa/Gallium3D hardware drivers and other areas of Mesa's massive code-base. There are also a number of fixes for the Mesa software rasterizers with Piglit.
More details can be found via this mailing list post. In total there are just under 50 fixes for Mesa 11.1.2.
For those seeking out all of the latest Mesa features, that work is building up for Mesa 11.2 that is entering feature freeze at the end of next week with an official release due next month.