.NET 3.0 will be released with Vista. It will not contain C# 3.0, but will ship with C# 2.0.

The major features of .NET 3.0 are: Windows Presentation Foundation (WPF), Windows Communication Foundation (WCF), Windows Workflow Foundation (WF), and Windows CardSpace (WCS, formerly “InfoCard”).

Visual C# 3.0 will be released as a part of the next Visual Studio release.

C# 3.0 will include features like:

Implicitly typed local variables using var keyword, e.g. var i = 5; would be equivalent to int i = 5; and var numbers = new int [] {1, 2, 3}; is equivalent to int[] numbers = new int [] {1, 2, 3};
Extension methods – static methods that can be invoked using instance method syntax (VB.NET developers have enjoyed having this feature for some time now, albeit with a compile time warning)
So called “lambda expressions” -- anonymous methods, which allow code blocks to be written “in-line” where delegate values are expected
Type inference – attempt to deduce argument type when one is not specified during a call to a generic method
Object initializers -- property setting during object construction, e.g.
Point p = new Point{X=0, Y=1};

LINQ (language integrated query) .. not happy with that!, linq = great
Etc.
For complete feature list and examples, please visit http://download.microsoft.com/download/5/8/6/5868081c-68aa-40de-9a45-a3803d8134b8/CSharp_3.0_Specification.doc

ref
http://blogs.msdn.com/irenak/archive/2006/08/07/690888.aspx