They say they're semi-permanent, but I dont think they will ever actually disappear. I'm supposed to get them topped up once a year to keep them at their best.
But being a goth (or something like that) I draw my eyebrows on anyway, so I've just got them tattoo'd the way I draw them, as opposed to shading of real eyebrows (see my avatar).
I have to say, it was the most disappointingly painless tattoo I've ever had. I could quite easily have fallen asleep while she was doing them. May have to go get a real tattoo now to make up for it! lol!