Very often users just create an account to upload unnecessary or unwanted files. We delete around three of such files on Meta per day (cf. http://meta.wikimedia.org/wiki/Special:Log/delete), and on other projects this is a problem as well, because in most cases there is no license or source provided and the files have to be deleted. People just come and start to upload their stuff immediately.
Of course, all wikis must be allowed to opt-out of this per community decision, but anyway. It should be default that uploads are enabled only after 4 days (just as page moves). It maybe needs an official note of the foundation on this, I don't know. At least, I would be glad to get one.