Well I'll agree with what Jon said, but I've flown with my tripod several times in the last few year w/o any issues and carried it on. While you will have zero issues if you check it, it could get stolen. I have a really old set of Bogen legs (10+ years old) that I put a strap on and have a RRS BH-40 on it. I fly with my LowePro Stealth digital 650 packed with all my camera gear, and the tripod on my shoulder on their straps.
When I get to security I just set them on the conveyor belt and send them through.
When I check in I keep both as out of sight as possible.
When i get to the gate I keep both as out of sight as possible.
I figure if they try to take it from me I'll either try to go back and check it (sperately) or if I can't do that I'll take the ballhead and strap off and "give them" the legs since they are old and I can use a new pair anyway... But since it's not written down anywhere that you can't take them on the plane I see no reason for them to say anything. How is it any different than a can that grandpa carries... And they can't say who's carrying it cause that's profiling....
Good Luck!
Oh, I'm planning on getting a small bog/sleeve for it though so it's less obvious as to what it is... But I'm not sure that will help at the Xray, because they've never given it a second glance there because it's so obvious what it is.
Ben