I've done it quite a few times, as a way of understanding how the photo ID requirement works. What would you like to know? In my experience, yes it really was trivial to fly without ID, as long as you're prepared to go through the SSSS + dump-search experience. That was all before 9/11, so I can't guarantee things haven't changed.

In my experience, when I said that I forgot or lost my ID, they typically didn't blink an eyelash, but when I said that I have ID but was refusing to show it on privacy grounds, I frequently got a ground security coordinator (is that the right term?) treating me in an unpleasant, disapproving way and asking questions like "do you want to fly today?".

It's quite an educational experience to demand your rights like this. I knew I was in the right (I did my background research -- I even got confirmation from the FAA that I was allowed to fly selectee, if I didn't have ID). But even though I knew I was right, I still found it very difficult to resist the pressure to conform, when faced with authority that was determined to treat me as some kind of horrible person if I didn't want to show my ID. Perhaps I just have a meek personality, or perhaps I'm overly affected by disapproval from a legitimate authority figure, but I found the experience intimidating and stressful. Looking back, it doesn't make any sense why I should be so intimidated when I knew I was in the right -- when I try to write it down, it sounds downright irrational -- but I did not find it a pleasant experience. It sure was educational, though.