Of COURSE it depends on the rider. Here's the problem: when I'm in a 30mph paceline behind some tri-guy I don't KNOW him or how good he is. So I have to worry if I'm going to wind up in a tri-guy pile-up.

It doesn't bother me until they hunker down on their aero bars in a fast paceline. In my opinion that shows a tremendous amount of oblivious disregard to the safety of fellow riders. Can't stand it. Other than that, no issues with triathletes. Hell, they LOVE to take stupid long pulls. Nothing wrong with that.