Here is a short but sweet one. It says the bubbles develop between 6-9months and are filled with water, not air. If they were filled with air the fish would have a hard time staying off the top of the tank. I never owned them but it does seem they have a few more health issues then other goldfish types. Basically, make sure there are no sharp objects in the tank. If the bubbles bust the fish won't necessarily die. It could get and infection or it can heal up too.
http://animal-world.com/encyclo/fres.../BubbleEye.php

Hope that helps a little, I'll try to find a better one when I have more time. It seems that that person at petsmart had no idea what they were talking about.