I have never once been told I wasn't able to take picture by a CM getting onto a ride with my big DSLR strapped to my neck. Of course I see the signs all over regarding flash photography and follow those rules. Heck, I don't even use my flash and don't think I have fired mine off on this camera at all.
Now Universal and Disney both have somewhat of a different policy when it comes to cameras on rides. For example you wont have an issue bringing it on Thunder Mountain but on the Mummy, No way Jose!