I've been using Mac OS X since December of 2002, and it has become my favorite. I'm using it as my main desktop machine now. I really didn't expect that. I bought the iBook only to learn a little bit about Mac OS X; I never expected to fall in love with it! Apple has done an incredibly good job of blending their UI with Unix. It isn't perfect, of course, but it's more than pretty darn good.
I suspect that the future of both Unix and Apple has only been improved by this. Developers who might have seen the Mac or Linux/Unix market as individually too small now have something much larger to attract them. Individual users who discover Unix by way of Mac will also have new worlds opened up for them. It's exciting, and it's fun.
Also see Mac OS X