should be fine!....
Don't flame me for posting cause i have an ibook, not a powerbook. I know my machine (that i love) may seem inferrior to you PB heads, but I think the same principles may apply.
In the new apple portables, the hard drive armature gets locked in place upon Shutdown and Sleep. When you put your PB to sleep... just wait a few seconds before hauling it away to prevent the head from skipping off the platter.
BEWARE of your laptop bag or a sensitive clasp. If your PB opens while it is in the bag it will wake it up and it WILL overheat in a bag, or the magnetic head will break off it is bombarded by shock.
As for the keys touching the screen, beware. Over time pressure from the keys is bad for the screen (though nowhere near as much as a problem on the newer PB's.... but still there). I use a folded paper towel between the screen and the keys. Just make sure you use something soft and NOT TOO THICK.
As for the X-Ray thing..... Theoretically possible but highly unlikely. If you don't want to be the one in 500 million people to possibly suffer such damage from X-ray acceleration of a moving electron on in your computer, then turn it off. I would leave it asleep... Anything to keep the flow through security and give them less time to get the idea to take it apart.
David