I installed OS X on an SSE3 system and it was pretty buggy. I was able to get the hardware to work, though. I even shared an internet connection with a Windows PC through a LAN crossover cable between them (which required absolutely no tinkering other than plugging them together, suprisingly). However, either I was using the OS incorrectly or else it wasn't working properly, because I couldn't seem to install any software.
Oh, and did I mention I hate OS X? I wasn't really committed to the experiment; I was just curious if I could do it. But that surely undercut my success.
OS X is really easy, though, to illegally install on any SSE3 system. Other than curiousity, however, there's not much point to it.