C# 4.0 (dynamic types, optional parameters, named arguments, covariants and contravariants handling)

New features of C# 4.o are presented in several places.
Ironically the most exposed is Doug Holland's at Intel's blog site :) - nice and very brief overview.
More info at Channel9 video provided by C# GoF :). The most striking facts are:

1. dynamic typing is for better Office interaction,
2. optional parameters and named arguments are evil, provided for VB developers to ease Office development in C#,
3. covariance and contravariance are only interesting (good) changes in language, but it should have appeared in previous versions of C#.

Additionally more about covariance and contravariance is on Eric Lippert's blog and more about dynamic programming on Chris Burrows' blog.