With the new explosive-detection machines, they usually ask you if you have any cameras or film in your checked luggage before they run the bags through. At least, this has been my experience.
I used to carry my film (mostly 200 or 400) in a lead bag until I discovered that the bag had a crack in it. Since then, I've just carried it in my backpack (carry-on) and have not had any problems. We've recently entered the digital age (have to send baby pics to grandmom on a regular basis), so I guess I don't have to worry about this anymore.
Funny thing about the lead bag: You would think that the x-ray machine would not be able to determine what it is, and that they'd want to hand-inspect your bag. Of all of the trips I've taken with it (probably upwards of 20 flights), I've only ever had to open the bag (and actually turn on the camera) once. Sometimes they ask what it is and then take my word for it. Sometimes they do nothing.