I dunno about carrying on a tripod, particularly a large one. I have always put my tripod in my checked luggage when I have flown, because I don't want to get to the security area/gate and have someone complain and make me check it. If I check it outright, at least I can put it inside my luggage where there's some protection. I wouldn't want to check a tripod "naked".
I agree with cliff re: "security through obscurity". I am also pretty sure the vast majority of people who see a tripod cannot identify it as being particularly valuable. Most people probably assume all tripods are in the $50-100 range, and have little clue to identify one from another. For just about everyone save dedicated photographers, seeing the name Gitzo, Markins, Manfrotto, Feisol, etc means absolutely nothing to them. I know it's not the best philosophy, but is there really an alternative?
I have heard of people getting by with smaller tripods which they can fit entirely inside a carryon, however again this can be up to the discretion of the TSA agent who sees your bag in the x-ray.
I have installed spikes on my tripod instead of the rubber feet and I'm pretty sure if I tried to carry it on I would get grief about it being a "weapon", particularly when you can't even bring box cutters or plastic knives onboard...