Looks like learning the workings of LLVM is moving only up and up on my todo list.

I thought there were still serious problems with NaCl on x86-64. http://groups.google.com/group/native-client-discuss/browse_... gives a brief overview, and there's been no word since that post, which was just over a year ago. I believe the problems have to do with NaCl's dependence on the segment registers; if I recall correctly, the APIs for manipulating them are the ones that were dropped in 64-bit Windows.

One of the links in this post is a paper that explains how NaCl is implemented on x86-64 without segmentation.

This technology is shaping up to be ridiculously exciting.