Yeaa! suddenly it does
EDIT: the bugger worked for awhile and stopped again...
If you see the cartoon guy at the computer, then you probably are using a browser proxy that hides the referrer field in the http protocol. If you see the "don't steal our bandwdith" gifs, then you are probably not using a proxy or using one that doesn't hide the referrer field.
In any event, it appears that my original speculation was correct: these upload sites are only intended to be used with their associated forums.