I've used probably more x86 based UNIX / UNIX like operating systems than many people out here.
Let's face it, there's not a lot of folks who remember turning key switches to load CTIX over CTOS on a Burroughs XE-550. Yes, I know there are some who will remember this, and things even older...
What I'm getting at, is that of all the operating systems I've used, based off of a plethora of chips, motorola, x86, powerpc, pa-risc, alpha, sparc, of them all, Solaris has been the most stable and reliable.
I've seen Linux systems, using kickstart, loaded onto identically configured hardware, end up with different packages loaded, due to some driver quirk that made it not load during one bootup, and work fine on another. I've seen boxes that ran fine, while their identically configured system crapped out repeatedly.
I've taken those same systems, and using a jumpstart server, loaded them with Solaris x86, and ended with identically configured, installed (down to the last package, configuration, etc) systems. All ran stable, fast and reliably.
Try taking your own run at comparing an application written for the A.M.P. stack, and first run it as a LAMP stack, then run it as a SAMP stack. You'll find that the SAMP stack outperforms the LAMP stack, sometimes by almost 100% on the same hardware.
Take a look at the security certifications, the revamped TCP/IP stack able to process millions (possibly billions) of messages per second (depending on the hardware it's configured to run on).
Take a look at the proprietary hardware, including CMT technologies, or the new ROCK processor due out this fall.
For a company that has been so solid in the operating system arena, to also be leading the pack in some of the hardware innovations is simply amazing.
Anyway, as I said, I've used most of the available UNIX/UNIX like operating systems, and find Solaris to be the best of breed for most, if not all, applications. That's my personal 24 years of experience talking, not just empty marketing words...