Whilst we have numerous virtualization solutions available in the market today, none is as tightly-bundled as Sun's and Zones. With the new 08/07 Build, Solaris makes it easier to run Linux and its applications on Solaris running on x86 architectures.
Whilst this may not be enough to tempt switchers to migrate from Linux to Solaris, this is one feature that makes Solaris as a worthy alternative. Personally, whilst I advocate Linux, I am strongly gearing towards Solaris on the servers. On the desktop, it may take until May 2008 before we see if its ready for the desktop. :)