2) Book covers most the new ehancements introduced in Sharepoint 2010, where silverlight can play a role.
3) The best use of this book, would be to use it as a cookbook for developing RIA using Silverlight 4 on the Sharepoint 2010 platform.
4) If you have been developing RIAs for quite some time and want to add the Silverlight flavor to it, this book should be the first step in my views.
5) How to use this integration between Silverlight 4 and Sharepoint 2010 at various phases of SDLC is not explained in an elaborate manner.
Overall, in terms of Silverlight 4 and Sharepoint 2010 integration, I rate this book 6 / 10.