I agree with smorbs and believe it should be evaluated individually. My gelding used to be very uncomfortable about being touched in his private parts and used to drip urine (that was all before I bought him), but it all disappeared completely after he was lightly sedated and a huuuge bean was taken out by a vet. Since then, he doesn't object me touching him down there at all and I have observed that he, indeed, seems more comfortable when I have done the regular cleaning.
I don't use any sponges or special cleaning lotions, though, just clean, warm water, if really needed. Wouldn't want to disrupt the ph balance in such a sensitive place.
I have come a long way, to surrender my shadow to the shadow of my horse.