I'm all for the community projects idea. After all, blockland itself is all about collaboration, so I think we've got a few collaboratively thinking forum users.
Anyway,
I was thinking about this pixel tower thing, and I've come to the conclusion that this could be semi-automated with some PHP and nifty CSS. People could just upload images to a site where administrators can approve or deny them. If they were approved, they would show up in the tower and with stylesheets the blocks could be made to overlap appropriately. All this would be automatic ('cept for the uploading and approval). I will start testing things tomorrow.