As it's been some months since last testing the performance of LLVMpipe for running games, I ran some new tests of Mesa 9.2.1 vs. Mesa 10.1-devel (using the Oibaf PPA) on Ubuntu 13.10 x86_64 with an Intel Core i7 4770K "Haswell" CPU. Of course, LLVMpipe really isn't meant for gaming and if anything just for driver debugging and as a fallback for a composited Linux desktop, but this is a nice way to stress the stack.
There were no real performance changes to find for this Intel Core i7 Haswell CPU when comparing the Mesa releases with the LLVMpipe Gallium3D driver.
The software driver also still only advertises OpenGL 2.1 support, but is close on GL3 compliance. Besides being used by Mesa developers for debugging purposes and testing Gallium3D, and then being used for Linux desktop fallback sessions with Unity and GNOME Shell, it also works well for teaching exercises -- but certainly not for gaming.