Today I looked in the archives and found a podcast from June, .NET Rocks episode 877, Kathleen Dollard Looks at .NET 4.5 Beyond Async.
The big thing about .NET 4.5 that everybody talks about is Async. But there is a lot more and Kathleen describes the portable class libraries, Event Tracing for Windows and more. They also discuss the danger of this being an inline update. Since the podcast was recorded 4.5 has been released and there is a lot of information on what it breaks and how to update from 4.0.