<p>What are the coolest new features that you guys are looking for, or that you've heard are releasing in c# 4.0.</p>

the dynamic keyword looks like it can bridge the gap between dynamic languages like IronRuby or IronPython quite nicely, which will probably help its adoption in the Microsoft monoculture... that excites me.
While I'm intrigued by it, I'm also worried that it will be overused, like Generics and LINQ, SQLCLR, etc :)