I write "Unix" almost exclusively for several reasons.

• I find "*nix" rather silly:
  • It doesn't even match "Linux", "HP/UX", "AIX", "Solaris", "SunOS", etc.
  • I think it emphasises the differences between Unices (and POSIX and other Unix-like operating systems).
• Writing "UNIX" would mean I was talking about something sanctioned by The Open Group, and I rarely talk specifically about such.
• I was writing "Unix" before the The Open Group or Linux existed.

I prefer to emphasize the similarities (and I try to ignore the differences when possible) and common heritage of Unix and the many systems that have been derived from it.

                - tye (and I'm not afraid to admit when Unix falls short)