For some reason, I seem to be very prone to smudging my makeup. To date, I've found only two mascaras that don't smudge on me (Lancôme Définicils and Kanebo Kate Dollish Long, if you're curious), and even MAC's generally excellent Fluidlines migrate after a couple of hours.
So I'm incredibly impressed with Gosh's Extreme Art; this stuff truly does not budge. I've applied it to my wrist and it's remained unsmudged through showers and hand-washing, for days. It comes off fairly easily with DHC Deep Cleansing Oil. I'm not sure how other makeup removers would perform. As liquid liners go, it's also fairly easy to apply; the brush it comes with is very fine, which helps.
I own it in black. From my point of view, it's a pity they don't offer it in a larger selection of subdued colours; the purple and copper shades look fairly wearable, but bright green metallic eyeliner is not really my thing.