I just returned from vacation to Costa Rica, where we went scuba diving. We had the HARDEST time with our scuba gear...the regulators and hoses were apparently just too befuddling for them. We kept telling them that it was scuba gear, but they still had to pull it all completely out of the bags, and then mess with it. This was a serious problem for us, because we don't want people messing with the setting, knobs, etc on our scuba gear...this stuff is very sensitive, and any kind of malfunction when you are 90 feet underwater can, ya know...KILL you.
But the thing that caused us the most problems were our backplate weights. These are just 6-lb metal strips with a bolt at each end - I can't imagine why they freaked out over them, it's not like they could be used as weapons, any more than anything metal could be used as a weapon (say, my blowdryer!). We carry them separate (removed from the Buoyancy Control Device) and assemble them prior to use. They were almost confiscated at EVERY flight...we had to BEG them not to take them! Without them we wouldn't be able to dive - they are a critical part of our gear. Not to mention they are custom-made, and very expensive - we would have had a fit if they'd confiscated them.
We carry our scuba gear with us on the plane because we are advanced divers, and our gear is just too expensive (not to mention important - it is, after all, live support equipment) to trust them in our checked luggage, where untrained hands might mess with them. But what a hassle!