OK, I have now purchased 2 of these babies, a beige one and a lavender one (I'm sorry I can't remember the names right now). I have used the beige one twice - it's a good enough dupe for Beige-ing, colourwise. The staying power is AMAZING. Today I wore it as my only base, went out for a walk in humid, "it's-about-to-rain" weather and my eyeshadow didn't budge an inch. And my lids are super duper oily - even with UDPP under them, MAC shadesticks or Paint pots can crease on me if it's slightly warm outside.
The Color Definer stick goes on smoothly, but you have to be quick if you want to blend it out with your fingers or something because once they dry the will not move. Apply it carefully so you don't get a too thick layer on your lid, is my tip.
I will definitely go back for more shades of these. I only wish they had them in black, now that MAC Sharkskin has been discontinued!