MAC made me fall in love with makeup — it was MAC pigments (which could have very well been fake MAC pigments, actually, given I bought them off of eBay), and it was pretty much a downward spiral from there.
For the most part, I organize by brand and then by product, but for brands that I might have only one or two items of, then I just sort by product type. I just like the way everything stores/fits when it’s sorted within a brand, since those products will fit well together.
If I do heavier eye makeup, then I use a separate eye makeup remover like Lancome Bi-Facil, because I find it’s easier to remove eye makeup first, and then remove face makeup. Then I don’t end up with eyeliner and green eyeshadow running down my face!