Take a look at the Deepzoom page composed by Rob Burke using AndreaMosaic and Silverlight Deepzoom. This is such a great idea and to me this is going to be the major use of Silverlight Deepzoom technology. I am not sure that how many other software available out there which does photo mosaic.
So I just tried to do one by myself. Bellow are the steps I followed
1) Installed AndreaMosaic and just follow the steps to create a photo mosaic file. You have to play little bit around the tool to undertsand what exactly is happening.
2)Open the DeepZoom composer (Can be downloaded here) and arrange your photo mosaics in the order
3)Export the Deepzoom project to silverlight project
4)Publish that to Silverlight Streaming service
and the bellow deepzoom Silverlight(multiscale image) has around 1000 images in it. Check this out by drag and scroll your mouse. Or check out theStreaming version here