This article sums up a lot of good points about Solaris. Userland is a joke, package management is awful, just installing and using the OS is an exercise in frustration for folks spoiled by the lovely tools available in a Linux system, but some of the core technology is amazing. He's not even mentioning the
other mind-bendingly great technology that Solaris offers: Zones. Zones are the most efficient and stable way to run many virtualized servers. Because they share a kernel and most system services, Zones can be extraordinarily lightweight, while still providing exactly the level of isolation you want. While Xen on Linux is nice, the smallness of Zones is a killer feature. Linux has vservers (and the somewhat broken fork OpenVZ/Virtuozzo), which use the same model, but the stability and capability of it leaves a lot to be desired. And, of course, Sun stands by Zones...problems actually get fixed, whereas serious memory management bugs have existed in OpenVZ/Virtuozzo for years (possibly also in vservers since they're derived from the same original source, though I haven't seen it, so far).
Anyway, a lot of Linux folks have written off Sun based on an old understanding of what Sun has to offer. If they continue to work on fixing the userland and the package manager (ideally replace pkg with RPM/yum or deb/apt, since both are remarkably better), and solve the driver issue (Linux has dramatically more drivers than Solaris...which makes a difference...a lot of folks like to have their target platform on their desktop, I know I do, and that's just not reasonable with Solaris), OpenSolaris could become a serious contender.
Oh, and dtrace. Holy crap, how awesome is dtrace? Can't forget dtrace. Sun has some serious engineers.