When I sign on with a new forum, I usually start at the beginning and work my way backwards to the present day, at least in the subforums I'm most interested in.
One that that persistently hacks me off is when a thread is full of pictures, and there's nothing but "404" images from Snapplefish, Phucketbucket, or someone's Angelfire space that went away years ago. Or in particularly annoying cases, when the thread is only a few weeks or months old, and the images are all missing.
I know that some forum operators prefer people to embed links to outside storage; it reduces the storage requirements for the forum, and it probably makes a sizeable difference on how much bandwidth the forum uses. But without the pictures, you might as well delete many of those threads, because they're meaningless without the images they refer to.
When I upload pictures to Gunco, as far as I know they're stored on Gunco. If not, I have no idea where they went... but Gunco seems to be able to hang onto them, because there are only a few threads here where images are missing, and most of them are pretty old.