Beyond introducing Gallium3D, Mesa 7.5 also brings support for several new OpenGL extensions, reworked two-sided stencil support, updated SPARC assembly optimizations, initial support for separate compilation units in GLSL compiler, and various other fixes and optimizations. Some of the OpenGL extensions now supported in Mesa include GL_ARB_framebuffer_object, GL_EXT_vertex_array_bgra, GL_NV_texture_env_combine4, and GL_EXT_texture_swizzle. These extensions are supported in the software drivers and then (sadly) just the Intel 3D driver.
The release notes for Mesa 7.5 can be found at Mesa3D.org. Unlike past releases where the odd minor version number indicated a development release and an even number indicated stable, that has changed beginning with Mesa 7.5. Mesa 7.5.0 that's now out should be stable, but Mesa 7.5.1 will come soon and that will officially be the stable version.
Next up in the free software 3D land is Mesa 7.6, which already will bring new state trackers to Gallium3D (OpenVG, OpenGL ES, etc) and Gallium3D networking support along with a host of other improvements. The Radeon Rewrite driver will also be part of Mesa 7.6 with support for OpenGL acceleration on the ATI R600/700 graphics processors.