Linux is UNIX. Why is there confusion around this?
RedHat linux is based on Berkeley BSD Unix. Originally, so were early versions of SunOS. Therefore, there should be no getting around the fact that linux is Unix and that the markets are the same. Regarding Solaris (SunOS starting at version 5.0) its roots lie in AT&T's System V release 4 version of Unix. Sun made the switch to get around scaling limitations in BSD. The new Solaris kernel was jointly developed by Sun and AT&T. Solaris' ability to scale vertically and manage very large address space is legendary. Linux will have a hard time getting there given its BSD roots. The primary differences between Linux and Solaris lie in the kernel. That's it. Virtually all of the user land layer is the same.
So, to all of the linux fans out there: When is the last time you had a conversation with your RedHat rep regarding backwards compatibility, futures, quick turnaround on bug fixes, indemnification, support pricing, and mission critical production support? I talk to my Sun rep regularly.