There are a few machines running in our CS department at Duke with Solaris on x86. But the main reason they're running Solaris is for smooth integration into the large installed base of Sun Sparcstations floating around campus.
Sun does a good job keeping Java up to date on Solaris (on par with Wintel), so if you're doing Java development, it should be great.
But on all of the research machines the department generally goes with FreeBSD; it's lighter and faster and more experiment-friendly... People have more experience hacking the internals...
Kyle