Although the "professional book" is suggested as a follow-up to this one, IMHO it is better as a reference guide. There are chapters that add little to Imar's book and others that go very deep. There are no practical examples, it is all theory.
I must confess, I was disappointed after being so impressed with Imar's book. I think it is a good reference but not really a follow-on book to "beginning asp.net."
You might like to take a look at the ASP.NET 2.0 Instant results, as this is a practical guide to quickly setting up particular applications such as a guestbook. I would like to see an update to this, to include such things as LINQ, the newer controls and the Entity framework.