[File under "Cool Presenter Tricks"]
Simon points us to Shyam Pillai's "LiveWeb" add-in. Run the setup there and PowerPoint will offer a web page embedding feature.
I must say I'm impressed, and already thinking of ways I can spice up my own presentations. With the add in, you can link to local or remote web pages and have them display as they would in a browser, within a PowerPoint show. You can event scroll the pages and click on the elements.
Of course, the main point of Simon's post was to mention that you can link to XAML pages (such as .xbap and .xaml), but the fact that I can include local or live web pages in my presentations is very cool all by itself.
In the above screenshot, I've (quickly) wired up a slide to point to Charles Petzold's "Teapot" .xaml example. Though as Simon mentions, there's room for extensions/options, I'm happy to say it otherwise "just works".