Some techniques used:
Background processing was used to do the heaving lifting.
For example. Users can upload large pdfs and videos which are then added to a background process for conversion to web viewable formats. Users can continue to user the site while these assets are being processed.
Image viewer for image magnification function similar to google maps allowing users to zoom in on a bill board image and read the fine print to be sure the wording and fonts are correct.
Image notations (like flickr and facebook) for detailed image discussion.