I agree, IQ doesn't really test any acheievement and even if it is supposed to be testing potential, who's to say that you can reach it or that it's applicable to what you want to do.
About 2 years ago, I happened across one of those internet IQ tests. I took it and scored 143. I figured this must be some stupid internet test, so I went and took the MENSA test, and I passed! (The administrator said the means my IQ is 135+ or 98th percentile of the general population) Then I took the MCAT, and while I did decently (30), that is certainly far away from the 98th percentile, even if the people who take the MCAT are, say, twice as smart as the general population. My GPA definitely confirms I'm no genius either. Maybe I'm just a lazy one. Anyway, I put it on my app because it can't hurt to have them think you're smart, right? 😉
Just my two cents.