I previously purchased 'Introducing Microsoft Silverlight' by Laurence Moroney, and it was fine for its time before Silverlight 2 was released. However, do NOT buy any book not based on the release version - way too much has changed from Beta 2 and you will be quickly frustrated.
This was an excellent book! But...first the bad. I think it was a little too basic in parts, particularly when it tried to teach me how to program in C#. One book should not try to be both a beginning tutorial and address advanced topics, which this does - I would have much preferred a lot less basics and a little more in-depth explanations. It was obviously rushed through to production because the graphics did not match the text in many cases, and there were obvious bugs in the examples that would have never compiled, much less work correctly. However, it all got the point across very well. I am not a great fan of 'let me show everything with examples' - I would rather have more meat and explanations. This book is BIG on example code, though - which is good in the advanced topics where you can have exact syntax to copy and play with.
Now the good - this book is very thorough, although it occasionally leaves out simple subjects (how do you upload a file to a server???) The examples are thorough, and Bugnion talks through most lines of code. He also covers almost all of the controls available in 2.0, and he even discusses the object hierarchy, which is invaluable when creating your own controls.
Expression Blend is thoroughly covered, as well as significant tutorials in how to code in Visual Studio 2008. This book is meant for a C# programmer who is interested in building n-tier Silverlight applications, not simple eye-candy. Integration with JavaScript and the browser DOM is also given a complete discussion.
In summary, this is the best book out there so far. If you are a C# developer looking to get into this Silverlight 'stuff', don't hesitate to drop a few dollars on this book. As an aside, Flash completely fried my brain - it is a designer's tool, not a developer's tool - and I despise it! Silverlight tends to lean to the developer, but still allows you to do all the cool stuff. In my opinion a perfect compromise and this book reflects that attitude by covering the coding as well as the design aspects extremely well.