I just read this whole thread!!! This is really great information to have for you and others who are looking to work at a mac counter.
A few things I did notice is that you do not need to have counter experience, but if you know MAC in and out, that usually gets their attention. One of the things that helped me land my gig about a year ago was visiting this site, as well as makeupally for techniques, product info and launches, etc. Trust me, when you know about a collection coming out before the own counter employees do, that gets their attention!
I say focus on what you are really really good at and build on that. For me, my strength has always been matching foundations, working with people of color, and natural yet flawless looks.
Also, another poster mentioned a few key things that you should know before going for your demo. I had my manager watch me and giving me tips so I was lucky. MAC is very peculiar about the organization, sanitazion and placing of products on your work space. If you have a couple of hours, do what I did, and hang out at the counter and watch the artists (if they dont mind). Ask them questions afterwards. It makes them feel like they are teaching you something as well as creates a bond between you and the artist(s) so they get to know you and your passion for MAC. It also leaves you with plenty of knowledge for the next time you go for your demo.
And I've said this on another board and I'm saying it now...MAC's hiring process is really really ...hmmm, interesting. Some SAs have that holier than thou attitute and are bound to mess with you and turn this into a never-ending process. LOL. Reminds me of when I pledged. Uggh.
Good luck sista gurl!