Long version: I picked up a bunch of rolls today from the photo shop, including shots from just before Thanksgiving through to New Year's, I think. I haven't gone through them yet. Hand-written on the front of the bundle of pictures was the cryptic comment "unable to scan roll properly." The guy working there tried to figure out what it meant, but I hadn't asked for a CD with my photos, which was his first thought. We went through them. One of my sets of negatives had a tidy, thick wavy line going all the way across all of them. He said they were caused by X-ray machines, and that one should never pack film in checked luggage. More to the point, he called everyone else working in the store in to admire it. They all said they'd never seen X-ray damage anywhere near this bad on negatives before.
I've never had any problems with this before. I've probably sent dozens, at least, of rolls of film through in checked luggage, and they've all emerged unscathed before. These pictures thought, well, they really didn't turn out all that well. There are some good pictures among them, if you ignore the grotty section waving its way through the middle.
There's a further irony here. They're all from Thanksgiving, and I know I didn't take any already used rolls with me on my Christmas trip. It's only this month, however, January 2003, than mandatory X-raying of all luggage in the US went into effect, and the rolls which travelled this month came out just fine.
Anyways, there you go. Feel free to learn from my experience, if you like your pictures the way you intended them, or else, if you keep trying persistantly, and want some special effects on your film, keep on packing it in your checked luggage.