i'm running freebsd 4.9rc -- smp is supported and runs, but i haven't tested whether or not it performs to full advantage. it is supposed to be improved in 5x.
to anyone researching os alternatives, i'd suggest at least trying freebsd. i've been very pleased so far. package management is nice (similar to debian from what i understand). you don't have to worry about all the sco lawsuit stuff going on right now, nor the novell/suse or redhat/enterprise wierdness. from various benchmarks i read, freebsd ranks near linux's 2.6 kernel -- but freebsd has already been out for a long, long time. it's established, and isn't likely to change it's "business model " down the line...
which leads to os x. i'd also love to see more support for os x as it is my other favorite os. it would be my prime candidate for server, but it's so new and so expensive that it's not an option for me... but it is freebsd based.
incidentally, my boss was told by oracle's tech support that the latest version of oracle will only run under redhat advanced server (which is licensed for somewhere in the ballpark of $4k) -- not any other distributions. this is news to me. maybe redhat's support guy is nuts... has anyone heard this, and if it's true, does it also have any affect on oacs or the community?