Even if it's never officially released OSX is based on BSD so it's almost inevitable.
Without having to rewind back to the BSD's, Mac OS X is built on the Darwin core, which :
- has been open-sourced by Apple,
- has been available for x86 for a long time (http://www.opendarwin.org
The Mac OS X GUI - which is probably the most interesting aspect of the system, because this is what differenciates it appart from Linux or FreeBSD - is not included in Darwin.
Anyway, a hack to run OS X on non-Apple computer is very likely to surface. How well it will run on non-Apple computer is still open to guessing.