If I could only pick two sessions, it'd have to be these:
Anders Hejlsberg: The Future of C# and Visual Basic
Bart De Smet: LINQ, Take Two – Realizing the LINQ to Everything Dream
The C#/VB session is a given, it's what most of us write programs in for .NET and it's everywhere; changes to these languages can change everything about how we program.
The LINQ session should also be pretty good, although perhaps a lot about rehashing things. LINQ solved the "impedence mismatch" between the different triangular (XML/XSLT/XPath), rectangular (RDBMS/SQL) and circular (in-memory object graphs) data but for circular, in-memory queries, the performance mismatch between LINQ to Objects and imperative old-school code remains in effect, even though monadic comprehensions have huge potential for optimization. I hope the PL guys have some thoughts on that as it sticks out like a sore thumb.