xRez have created a very interesting project that utalizes Silverlight Deep Zoom with data on the Yosemite National Park. Basically you are able to 'drill' down into the map and you will notice 20 'hotspots' that are identified by a picture. You can zoom into these pictures and admire the 45 gigapixels that are available. The Silverlight version can be found here.

xRez have created a PDF of the project proposal that you can view here, along with an explination and some sample images of the data used which is located here.

Here are some screen grabs of it in action

This is a great example of how powerful Deep Zoom is and I can't wait to see future versions pushing the boundaries even further!