This may sound like an odd answer, but I'd lean towards 100%… Simply because of a larger conceptual argument – if you're not enjoying it, it's not sex.
That said, the pain and frustration issues around willing receivers is common to men and women – how do you "relax to fit" in a situation where the orifice/passage are not self-lubricating? This challenge, and discovery process leading to a satisfactory answer, seems to be "too much work" for a lot of women (and men, for that matter), which leads many to think that because their initial attempts were painful, it's just always going to be that way.
Getting an idea for how many people "give up" on anal sex before learning how to properly accomodate, plus those who genuinely dislike this form of stimulation, is very difficult to assess statistically.
About the closest you can get these days is to use the "practicing" numbers, and assume that people practicing anal sex do enjoy it (which is my original point, actually). For details on those numbers, try reading the great top answer to the question, by (D'oh!).