Wallace B. McClure posted here about some of the concerns he has regarding WCF. I'm not sure I agree 100%, but he does make a pretty good point about the fact that MS is pushing WCF pretty hard as a solution to all problems, and we'll just have to see how that turns out in practice. This, by the way, seems to be a common pattern across the
WinFX .NET 3.0 technologies.
I'm confident plenty of cool things will come out of WF, WPF and WCF, though I'm also certain that a couple of years of real-world use and one or two extra versions are going to provide massive improvements to the stack :-)