Just noticed a new article on MSDN from Scott Mitchell which pretty much covers everything you need to know about ASP.NET Viewstate. This is one of these ones which will become my first suggestion for people who have questions on this most mysterious and misunderstood of ASP.NET topics. If you are an ASP.NET developer you just have to read this article - I promise you'll learn something from it!
Oh, he also links to one of my blog entries on compressing Viewstate...which I am sadly chuffed about :-)
UPDATE: Just noticed that Scott posted on his blog about this article - also interesting stuff on Google AdSense