Maybe, Solaris people tend to be rather elitist about their OS.
SMP works really well, actually Mandy shipped 8.0 to autdetect for a second precessor and install a different, SMP enabled, kernel if it saw one.
I've got 2 SMP boxes running right now... an old SS10 and a Dualie PPro 180. Some things that usually come pre-configured for SMP: XFree86 4.0.x and above, KDE 3.0.0, at least as I've seen it on Slack and RH, Grip which might sound small, but mp3 encoding is processor intensive, so being able to split it is a brilliant thing, fluxbox... a lot more, its usually the default these days as if the additional instructions aren't needed they're ignored.
Usually though an out of the box distro will require a kernel re-compile. Slack comes with a pre-built, I think RH does as well.
There are quite a few guys running SMP Linux systems with the AMD Tyan boards, cost ballpark $200, then another $150-ish per chip, and the RAM for the chipset is a little expensive compared to just vanilla ddr that you can drop in any board, but its a whirling fun investment.
For instance, I was swapping chatter with a guy on a thread here about his dualie AMD XP 1900 board, 1 Gb RAM, so of course his soundcard didn't work,

He had kernel compiles down to 55 seconds.
My crate is a no slouch AMD 1.2Ghz T-Bird with 768, but I could never really make it under 3:00.
Anyway,
Cheers,
Finegan
Not only that