I just got into MAC this summer - I can't really remember what triggered it, maybe it was the Pigments? I was trying to get as many of the (now extinct) Tony and Tina Universal Colour Dusts off Ebay, before they were all gone forever. Somehow I must have heard about the pigments, and went in to take a look. Well, about a month and I'm sure close to $500 later, I'm feeling a little obsessed.
I am incapable of true makeup fidelity, though. With my fickle heart, I like to flirt with Clinique, Dior, Shiseido, Lise Watier, and even have some Bonne Belle pallettes (amazing payout for the price!). I'm sure I'll always have more MAC than anything else, from now on, though. It really is among the nicer products I've used (although Dior and Shiseido are completely amazing, too).