My first tour (which I just finished a week and a half ago) I didn't use a triangle, but I did have a neon jersey that I wore every day. And it helps a LOT. Like people said, no one (well nearly no one) wants to hurt you, it is more a matter if they can see you in time to react correctly. I think a neon jersey would be very important even with a triangle, simply because you body is higher up than the triangle will be, and that is very useful in hilly areas.
And don't even think of touring without some sort of mirror (unless you have perfected turning your head and keeping straight, and even then, I would recommend a mirror), you just can't expect all drivers to know what to do around a cyclist, so it is up to the cyclist to be on the alert about EVERY car that is going to pass you (unless you got a nice 6 feet of paved shoulder, like I did in Kansas... that was a great state to cycle through). On my tour I was only surpised be a car passing a couple times (all of them were on very hilly Missouri roads).
Sorry if that came off a little strong, but I believe safety is of the highest importance. Not much point on going on a tour if you get in an accident in a few days.