Sun Solaris 10 holds more than 100 world records in performance.
Everybody can register and download a free version for his platform (versions for the most common platforms are available).
Setup is not complicated for experienced users.
This operating is best for .com grade sites, many sites and companies are powered by Solaris. It is powerful operating system with high security level.
A lot of tools come on free downloadable Solaris 10 Companion DVD, it has compilers, alternative print spooler (CUPS) that is much easier to use that the original one.
You can choose to install Solaris Management Console, which I highly recommend, allows to manage users, groups and computers from GUI.
Still, a lot of functionality, like services have access only from terminal ("command line").
Solaris 10 comes with CDE desktop (based on old Motiff) and Java desktop which is much more friendly and Windows like and has more functionality, but works slower.
Solaris can work with a lot of tools and programs that are built to it, like web browser Mozilla (unfortunately not all sites support it, and it have some printing problems with page division), Studio 11 (great tool for software development), Open Office and much more.

In summary, it is great operating system, probably the best available for servers, but still lacks applications for home users, thats why I rate ease of use 6/10.