Some email ask me how to learn OBA efficiently rather than learn them all of Microsoft Office stuff in "Microsoft Office Developer Poster"..the answer is depend on what solution that you want to build But if you want to learn OBA efficiently try this links..
Happy Fasting month and of course happy coding
If you see MSDN site, Silverlight is now come to the production stage..well after playing for a while this day, the backward compatibility with RC seem good...and no more blood tear just like when you migrating from beta to RC version...what a mess 
ah and don't forget to download and inttall them..here