our twin boys at daycare came in matching long sleeve shirts yesterday. they're identical except for a birthmark on one's arm...which was clearly hidden. One has a freckle on his face, but it's so pale I can't really see it, at least not from any sort of distance.

they often wear the same thing in a different color, which isn't so bad. you get used to it after you initially figure out who's in which. I wouldn't do it for my kids because it's just double the clothes to buy-if you never dress them alike, then they can share when they're little.