Mesa 7.4 Release Candidate 1 contains additional bug-fixes on top of Mesa 7.3 along with a few new (though relatively small) items. Mesa 7.4 adds a MESA_GLX_FORCE_DIRECT environmental variable for Xlib/software driver and GLSL version 1.20 is now returned by the GL_SHADING_LANGUAGE_VERSION query. There are nine official bug-fixes in Mesa 7.4 RC1.
The Mesa 7.4 Release Candidate 1 announcement can be read on its SourceForge mailing list archive. The latest development release can be downloaded from the Mesa3D beta directory.
Meanwhile, the majority of the development efforts are now going into Mesa 7.5. Most notably what this brings is the pushing of Gallium3D into Mesa's mainline code-base. There are also new OpenGL extensions and other improvements. Mesa 7.5 can be expected later this year.