I haven't used Solaris since the 1990s. I remember having an Ultra10 and being amazed at what a different machine it felt like if I booted Linux/SPARC instead of Solaris/SPARC. (These were the days when "Ultra" meant UltraSPARC, instead of "AMD" as it seems to with the new Ultra20.)
I don't know if Solaris has improved. I was tempted by an Ultra20, but a friend who's heard one on the other side of a closed fire door tells me they're loud. Too loud to share a house with.
All the same, I was pleased to read If Linux is faster, it's a Solaris bug!, and can only hope that Apple takes a similar stance. Mac OS' file system caching sucks compared to Linux. On Linux, if you find(1) and grep(1) on a big source tree, it might take several seconds the first time. The second time around, though, it'll take a tiny fraction of a second. On Mac OS, no matter how many times you do the same search, it stays slow.
Perhaps I'd have to trade off some Mac OS feature to get the Linux performance, but I'd love to know what. (Spotlight may have made things slower, but not significantly, and my complaint isn't the worst-case performance, it's that the average is pretty much equal to the worst-case.)
I'd still probably make the trade on any development machine.