The Intel SNA acceleration architecture significantly improves the X.Org driver's performance over the UXA acceleration method that's the default. SNA has been in development since last year with much of the development being done by Chris Wilson of Intel OTC. SNA stands for Sandy Bridge New Acceleration, but it benefits all generations of Intel graphics hardware. SNA has worked out extremely well in recent months with all bugs appearing to have been squashed.
With the xf86-video-intel 2.20 release, SNA isn't the default, but now it's compiled into the driver without needing to build the driver separate while passing the --enable-sna switch. SNA can easily be enabled by just setting the AccelMethod within the /etc/X11/xorg.conf to SNA.
The xf86-video-intel 2.20 driver release alone brings 456 changes from Chris Wilson, most of them relating to SNA acceleration.
Aside from the SNA loving, xf86-video-intel 2.20 brings UXA acceleration bug-fixes and X.Org Server API compatibility improvements for X.Org Server 1.13.
The release announcement for xf86-video-intel 2.20 can be read on the Xorg mailing list.