This was great fun - I can see lots of possiblities for this on a personal level - not too sure about the public library computers though as people may need too much time to create the mashup (we have a 1/2 hour limit).
The voicethread option could be useful for our local history collection.
National Library of Australia has a mashup project on the go with Re- Picture Australia using selected images from different collections - they are inviting people to take an image and add 'artwork' and re-load as a new image. Instructions are at http://www.pictureaustralia.org/index.html.
