I did a 90 mile citizen's road race this weekend where aero bars are allowed. Rules state you can't be on them when pack riding or on corners (rule not always followed). I'm guessing out of 1400 riders maybe 200-300 had aero bars or some sort of TT/tri bike.

My guess is these folks would be as fast or faster without them (and pacelining), but like one guy told me at the start, "I'm not comfortable riding in a group". I guess I'd rather folks like that have the option to run bars "solo" than ride in front of me in a line.