Also, if you're NOT opting out of every scan, you're not helping the cause. You NEED to opt out of every single scan every chance you get, otherwise they'll eliminate the option and say "well, people seem to be OK with this since no one is opting out!"
Opted out at SFO and DTW and each time it was no big deal.
I go through security an average of about four times a month. I opt out any time I'm not in danger of missing a flight. Some airports are friendly and expedient about it, others (most recently, Austin) had me wait for about fifteen minutes before finding someone to do the pat down (while I tried to watch my bag/laptop/phone on the other side of the scanner).
Opted out at SFO and DTW and each time it was no big deal.