Doing what I can to test FBSD CURRENT. Getting back to PC assembly after a really long time too. Thinking about optimizing some of FBSD's libc for Athlon/Intel P3 and higher CPUs. SIMD operations for things like bcopy could be a useful enhancement. How many programs do you think call that anyway?
FreeBSD is a good platform to try this on since it is encouraged to recompile the whole system to get updates. If there is a good way to switch which implementation of certain libc functions get called it could be a nice enhancement.
Anyway that's what I have been doing in my decreasing spare time.