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Also, check out the blog of the developer who works on the GC, where there is an article about the new GC, plus a link to a Channel 9 interview regarding the .NET 4.0 GC.
Yes, lots.
My latest book Visual F# 2010 for Technical Computing includes a lot of performance-related information about .NET 4 as well as F# itself and the performance measurements and advice are quite different with .NET 4 and the new background garbage collector. In many cases we're seeing substantial performance improvements but there are some slowdowns as well.