You guys inspired me to conduct my own JPEG experiment. My tests and procedures can be found on my blog here, but these are my basic conclusions:

• An image that is repeatedly saved as a high-quality JPEG will degrade slightly, but only slightly.
• JPEG quality can vary extremely widely, and it only takes one save as a low-quality JPEG to seriously degrade an image.

The blog article also has links to all of the pictures I generated while testing.

~*I've made it my mission to build Cyberworld, one polygon at a time*~

Watch it happen at my technology blog, Building Cyberworld.