My GSD is pretty solid in the nerve area, nothing rattles him, shotgun blasts, firecrackers, new things of all kinds don't seem to phase him. He will show curiousity, but when told to "leave it" then he will just sit and watch. W/ the exception of my lawn mower and the snowblower, which he has torn pieces off of because when they are on he hates them. Anyway, I am coming into the house today with my 5 year old, she has a helium filled balloon that is floating around. The GSD sees the balloon and growls at the balloon, snarls, and then tries going airborne to get his teeth into the balloon. Is there something that I'm not seeing here? Is there something special that I ought to have known about floating objects that spins up working dogs? He did not hesitate, did not back up and look, he went straight for it before I could even get the 5 year old out of the way, we were not even 4 feet into the house yet.
Luckily she let go of the balloon as soon as we hit the inside of the door. Other than this he has always been fine, no freaky behavior at all.

Well your ballon incident went better than my blimp experience...

A family member got one of those large inflatable helium blimps that are remote controlled for a B-Day present... needless to say it went the way of the Hindenberg once my GSD saw it. There was an exploding blimp, a very proud GSD, and a crash of humans all tangled on the floor.

On the other hand, the same floating Blimp terrorized the family dog (a beagle mix). I guess the idea of something stalking her from above is more than she can handle. If she sees a ballon or any other object floating, she tucks tail and dives under the nearest chair or table.

I got my god-son one of those RC flying saucers for Christmas, and my GSD promptly decided it was Satan and that he had to protect the family from it at all costs. We barely saved it.

I once had a lab-mix who freaked out when let into the house after a party where we'd decorated the room with helium baloons with ribbon-streamers on them. We joked that she was afraid of the "evil sperm."

Dave - ditto on the RC saucer here! My daughter got two for Christmas, and we have to put Ceili away for Brianna and her friends to play with them - dog practically froths at the mouth to kill the saucers!

Ignores ballons and those Hoverdisc things, as well as frisbees. Maybe it's the whirring noise that convinces her it's a Very Bad Thing!