I considered including 64-bit Windows 2003 and XP (I'm pretty sure they're mostly 32-bit outside of the kernel), but my focus is really open source operating systems. Solaris is not open source, and it was supposed to have been released under an open license before now. Aside from that, I have been unable to get any kind of network connection on Solaris thus far on four machines -- I'm sure I'm doing something wrong with the network or driver setup, but I haven't dedicated any time to researching the problem yet. When Solaris 10 is open source, I'll include it in articles like these.
Sun told me at the Solaris launch that much of the userland will be 32-bit in 64-bit Solaris because they didn't see a need to spend time and money on making "Trivial" programs 64-bit clean.