One of the interesting changes is in the Cast<T> operator and its behavior is better described in this post by Ed Maurer. I think that the side effects of this change should be limited, because the use of explicit type for the range variable in a query expression (i.e. from int n in numbers select… instead of from n in numbers select…) is not very common. In fact, I don’t remember examples of its usage in our Programming LINQ book. Take care of this change if you used (or will use) this syntax.