Often, if i'm working on a simple website to show someone, i'll host it in the public folder of my dropbox site and send them a link to the public URL.
Today I did this with a site using jQuery and it wouldn't work. Turned out that jQuery was being blocked when loaded from code.jQuery.com. I changed it so that jQuery loaded from the google api site instead and it all worked fine.
Not sure if this is a typical problem but hey.