I would make the most terrible eyewitness.
I've watched the X-Men 2 movie twice, and I still didn't consciously notice that Nightcrawler only has three fingers on each hand, and only two toes on each foot. I mean, I guess I must have seen it, but it didn't really register. Then I read an X-Men comic ("God Loves, Man Kills" in case anyone is interested), and only through that I became aware of this rather obvious fact for the first time. My observational skills are truly pathetic.