I have to admit I would use the same word without worrying about it, but recently I was on a US forum and used it and I got a real flaming from a load of folks saying that it is such a bad word bit like the N-word or F-word, and very un pc to use it. The correct term apparently is "Intellectually challenged".
A wheel chair user used to be called a cripple, then handicap, now disabled, all of which are deemed to have negative connotations, and now I have seen disabled folks being called People requiring technical care.
Soon baldies are going to be referred to folliclely challenged. Is it all getting a bit out of hand?