I did this once in Charlotte (which btw is normally an excellent airport). I had to wait about 15 minutes for 'the agent' to show up that would conduct the pat-down. There were about 5 TSA agents standing around doing nothing while I was waiting. Setting aside the wait time, they were all friendly enough, but they all had this look of "ugh... what is this guy's problem", and I wouldn't bet against the wait time being a purposeful deterrent.

So, while I will continue to opt out when possible, I wouldn't recommend doing it if you're short on time.

I always opt out, politely but firmly. I was flying out of SFO once last year when a TSA agent asked me "and your reason for opting out is...?" and I answered "...none of your business." He smiled and from his response I inferred that he approved of and appreciated my response.

At first I thought my opt-out would be recorded, but most of the airports through which I've flown do not record anything about the opt-out. They just pat down the subject and try to keep the lines moving. I no longer believe this is an effective way of registering my opinion.

On maybe 2-5% of my trips it ends up being 20-30 minute wait at the same airports that normally take 3-5 minutes to find a screener.

As a result I still need to show up 20-30 minutes earlier then I would otherwise.

I did this about 4 times so far but then the last time it now up in my face by adding 1 hour to my screening time and while I philosophically wasn't too keep opting out I have to wonder if I can keep justifying it pragmatically.

How did it add an hour to your screening?

As netnichols stated above, "I had to wait about 15 minutes for 'the agent' to show up that would conduct the pat-down." I'm guessing that this is the reason.

I've successfully opted out once. In that instance, an agent performed a pat-down with no wait. I tried again more recently and, after fruitlessly waiting 5-10 minutes for the special pat-down agent to arrive, gave up and reluctantly went through the backscatter.

I always opt out.