1994: Had a Mac SE in a padded "carry-on" bag that had fit on the bins in one direction. 3 months later, they wouldn't let me take it on the plane, I argued and argued with the staff, but gave in and let them check it, marked with "fragile" tape. Hard drive died, no backup, computer ruined. The worst part: The airlines are not liable for damage to electronics. They are not liable for any valuables - read the fine print on the back of your ticket (or wherever they're hiding it these days). I would not check electronics, jewelry, or anything valuable.
Glad the rules changed, but I do hope this doesn't have to happen again.