If you are comfortable with Linux then Mac is an easy transition. It is basically a BSD core with proprietary junk added.
The big thing that I like about OSX/apple is that I get all the “power” of linux, but with commercial support that will help my wife with those questions that set marriages on the brink of disaster (“why can’t I open my email?” “Did you click the mail icon?” Why should I do that?" “To open email?” “But I don’t want to!”) while at the same time able to address the issues of the less casual user (“need to port from PD7 and am looking for …”).
As to the TCO, apple is not the cheapest IF you are willing to self support 100%. If you want to off load support then Mac is by far the cheapest solution out there IF you keep all MS apps off your system. Once you start putting MS products all bets are off as you office and its brethren stick you in the upgrade spiral no matter what OS you are running.
That said, I spend 90% of my day in windows for work. It is functional. But it is not easy. Nor is it efficient for my line of work (interfacing with LOTS of different systems most of which are unix variants). Even with that, I’m about to hang myself on a dell venue/ms surface style tablet. Real systems delivering the promise of true portable computing from the late 90s early 00s.
Linux just isn’t delivering in this format. Apple has a clear. different direction. They lose my $$ on this front.