Doing a little search on some of the new IE8 features, I found this page listing a series of IE8 whitepapers:
http://code.msdn.microsoft.com/ie8whitepapers
Amongst other things, you'll find documents on Activities, WebSlices and the Developer Tools.
Interesting enough, eBay supports Activities and WebSlices right now:
http://ie8.ebay.com/
