(Open)Solaris died a few years ago. It has got some great features like Zones and ZFS, and it's still very stable. However, they lost the hearts and minds of almost everyone. I used OpenSolaris for a few months as my desktop. They don't have the package support of Linux, or the large community. Gotta remember to get GNU Make before Sun's Make in PATH, Gnu sed before Sun's, or was the other way around, Perl CPAN modul…
I went to an OpenSolaris users group last year. They were talking about new network features like being able to assign sub-interfaces to different zones. Stuff that VMware ESX had available for years. I was thoroughly unimpressed. The concept of Zones or FreeBSD jails has some appealing aspects; not needing to load multiple kernels in memory, for example, but by this time, Hypervisors such as VMware that deduplicate…
Zones and ESX are very different beasts, and de-duplication of memory is only part of the issue when you're talking about virtualization of user-space versus hardware virtualization.