They claim to instantly delete them, but these aren't exactly highly paid technicians. Violates some child porn laws too.
Personally, i am more worried about the rays than about somebody seeing me "naked", but i sure as hell would never let my kid into one of those things.
My general view on these scanners is that, if the security staff on the airport would do their jobs right, they wouldn't be needed anyways, but as these people are normally pretty dumb and (at least in Europe) 50% of them are muslims so they probably give a fuck about terrorists, i'd rather have a technology solution.