Thanks to everyone who attended. I wish I was not so under the weather. Hopefully it was not too hard to understand me. I didn't want to cancel the webcast at the last minute. The deck from my presentation is here. The majority of the samples I showed are available in the gadgets section at http://www.visitmix.com/university/. The example I showed using ASP.NET AJAX to call web services is available here. Steve Marx has a nice walkthrough of the process of initial setup here. You can find out more about the ActiveX/WPF gadget I showed from Karsten Januszewski. Tim Heuer has a VS Template for Sidebar development here. I haven't used it, but most of the stuff Tim puts together is gold:).
UPDATE: As Tim pointed out, the maximum docked width constraint of 130px is a usability recommendation (not a technical one). You can, in fact, set the docked width of a gadget to be a much larger number, but it will look goofy IMHO.