I just bought this and it is FABULOUS!!!! i watched a mac makeup artist put it on my friend when she was doing a trial run for her wedding makeup and had to have it.
It's probably similar to the Stila smudgepot -- comes in a little jar and you put it on with a little angled brush -- kind of press it right into the lash line and then blend it out to create a smokey look. It is so easy to apply and stays workable so you have time to play with it before it is totally dry.
i was so sick of the eyeliners i had been using that were really hard and went on clumpy, and this is totally the best alternative to pencil liners. it's also a million times easier to apply than liquid liners.