It's been a while since I've posted. Most of the recent changes have not been made by me, but by Prakash Punnoor, who has nearly completely converted the build system to CMake. The configure shell script is still usable, but once all the features are converted it will likely be removed all together or stripped down to a simpler form and just kept for compatibility's sake.
Also, Prakash has imported an SSE-optimized version of the libvorbis MDCT. The new build system, along with asm run-time detection, have made this possible. The effect is a 5 to 10% increase in encoding speed.