EricRaymond used to say that linux was a unix like operating system. Then the owners of Unix tried to bully him, so he switched to saying that unix was a linux-like operating system. In this day and age, this seems to make more sense to average people anyway. I mention unix, they have no clue what I'm talking about. I mention linux and they have a vague idea.
In December 2001 ScottMcNealy called Solaris "our implementation of Linux". (http://www.zdnet.com/eweek/stories/general/0,11011,2662720,00.html)
See also: LinuxCommunity, LinuxOperatingSystem, UnixOperatingSystems