If you have two or more servers load balancing, are the servers mirroring one another? If images, etc., are uploaded, will they be stored on all the servers so that if one server goes down, the images will be served up by another server?

It all depends on how you set it up, but certainly you can do it the way you say.

You would want to put your data on SAN attached disk so that each of the servers could access it. Then configure your servers so that when one fails the server that takes over for it mounts up the disk that the failed one was using. You could even do something as elaborate as install a clustering product like Veritas Cluster Server which would allow all the servers in the cluster to mount the same disks simultaneously.