Airport X-ray security scanners do not cause any issues with iBook and PowerBook computers.
The American Society for Testing and Materials (ASTM) conducted a study on X-ray induced issues to memory devices, including audio and video tapes and floppy disks, and found that these devices have enough shielding to protect the media.
The study found that the magnetic field was actually strongest around the security monitor, which most computers never even come close to. They taped a disk to the monitor for several hours without harm. A committee member suggested that it would take at least 1000 million passes through the X-ray machine before any issues would be evident.