These performance enhancements target 915G/945G/Pineview graphics chipsets and speed-up the glyph rendering process, avoid using software fall-backs in some scenarios, better performance with large windows, and the driver now avoids migration ping-pong with gigantic drawing.
This driver has also been enhanced with GEM support for XvMC and the video overlay. Last but not least, there's a whole collection of bug-fixes and other work that has piled up into the open-source Intel X.Org driver over the past quarter.
The release announcement along with more details on this xf96-video-intel 2.12 release candidate can be found on the Intel mailing list. The final release of the xf86-video-intel 2.12 driver should come in the next month.