FWIW, flying out of my home airport (BWI)... The TSA seems to open and check bikes more often that not, unless I have just been unlucky. They do not seem to be very careful how the do it either. My carry on has been thoroughly unpacked and swabbed a couple times. My checked suitcase on the other hand has never been opened by the TSA.
I have never locked my bags, but do tape up the bike box pretty well.