I went to visual performing arts high school and one of my classmates was a counter-tenor. He also doubled as a baritone, which, from what I understand is fairly common. It was incredible what he could do.
In the UK you'll find a (relatively!) large number of countertenors, at least within the anglican church music tradition (I said relatively). Until quite recently all church choirs would have been solely male, with boy trebles and adult male countertenors. Female altos in these church choirs are still relatively uncommon.