Like most others have said, I'm not necessarily "disloyal," I just buy what I like from MAC and purchase what I like from other companies instead. More often than not, it's the price that pushes me away; I can almost always find a very similar product for at least half the price that will do the same thing for me.
I absolutely DEPEND on MAC's Rule eyeshadow and NW15 studio finish concealer for my horrendous undereye circles, and I like a lot of their eyeshadows, fluidlines, and lipglasses. But to be quite honest, I usually just use pencil eyeliner, I DEFINITELY prefer pigments over eyeshadows and can get tons of colors from other places for the cost of one MAC pigment, and there are tons of great lipglosses out there. There's no doubt in my mind that MAC is a great company, it's just hard for me to justify spending that kind of money when I'm in college and can find cheaper products of about the same quality.
MAC's foundations are okay, but I actually tend to prefer drugstore products better. I find a lot of their lipsticks overpriced, their mascara is nothing to write home about, and I am REALLY getting sick of the constant LEs.
I DO wish I could own some of their brushes, as I've tried out a couple and really like them, but they're just not worth the money for me.