I am not surprise Windows users don't like Solaris, because is unix and is difficult to use. Unix is like DOS, text base, do not have a easy to use installer. Some Windows users find that unix is difficult to use, because they can't locate where is the C drive, unix use a directory name for each data partition and not using alphabet to name the disk drive.
OpenSolaris release 2008.05 is free for download
I am surprise Linux users don't like Solaris, for the same reason -- Solaris is difficult to use. Even Linux and Solaris are unix base operating system, there are some minor differences. They have a different name for network device, the configuration file setting could be different, Solaris name their X-windows as openwindow, but basically both Linux and Solaris is quite similar.
Solaris is difficult to install. Yes, it could be difficult for new Solaris users, especially when they experience a driver problem (most common is the network driver problem). Without a rich driver support as Windows, install an operating system is always a problem. Linux is easier to install because the Linux users were using Red Hat 9.0, Fedora or Ubuntu. If these Linux users are using Linux since Slackware, they will have a different definition on what "difficult" means.
Install a software (including the operating system) is not really a big issue, it only need to be done for the first time, and sometimes it was done by the hardware engineer or system support engineer. The worst nightmare for software developer is, the piece of software that you write, keep crashing for an unknown reason, it could cause by your application, it could be the operating system, or may be is an unstable system API call in your coding.
I use Windows, I use Linux and I use Solaris. Solaris is my prefer software for server end operating system because Solaris is very stable. I have experience on using Solaris to run heavy loaded software for years without shutdown, it has good performance while running on old and low end Sun machines, eg. 50Mhz sparc CPU.
Sun Microsystems has release Solaris as open source and free for use, that is OpenSolaris, and it runs on x86 platform. So is easy for software developers to try it on their machine. The latest is 2008.05 release, available at opensolaris.org website, try it out today.