The only real problem is that Silverlight 2 currently only supports a limited set of mouse actions - and the mouse wheel isn't there. Luckily I found some code from one the Expression team that solved my problem (though I did manage to learn about using C# anonymous delegates as event handlers along the way...). That's what really took the time, but it's given me an application that doesn't need a key press - just a mouse. Click and drag to move around, and scroll to zoom in and out.
[Edit: I've added code to zoom in on a mouse click and to zoom out on shift-click]
So what did I do with what I learnt (apart from writing 3,300 words of magazine tutorial)? As it happens I have a pile of images from a trip down into the Large Hadron Collider at CERN. A collage stitch of my images of the ATLAS detector, down in its cathedral-sized cave, comes in at a hefty 28 megapixels - a little large for Flickr or any other photohosting site. However that's ideal for building a Deep Zoom.
Here's the application I built.
Zoom in and you'll see the engineers at work, and read the text on the eight superconducting magnets that surround the detector core. I've seen things in there I didn't realise were there at first!