Ok ok, I've bitten the bullet and upgraded the Twitterlight Silverlight Twitter client to Silverlight 2.0 Beta 1. The Coding4Fun article has been updated with the latest source.
The client is live at twitterlight.com.
The major updates involved changing how some of the synchronous web service calls (authenticate, create TinyUrl) work within the app, now that all web references (woops, "service references" now) are asynchronous. Some XAML tweaks and minor code changes, and we're good to go.
View the initial post describing the article.