The primary reason to run Solaris is to have access to the broad base of Solaris ISV and IHV products.

OpenSolaris will is incompatible with Solaris in many notable ways. (e.g. uses GNU for libstdc++.)

Losing free Solaris x86 means I can no longer recommend it -- not when CentOS, a 100% ABI-compatible RHEL clone, exists.