A little note to the new developer that is just getting into writing Extension Methods in .NET 3.5.  Your extensions will not show up until you compile your static classes.  This should be obvious to most but the Visual Studio 2008 IDE does not precompile the extension methods while you are coding.  It does this for all your other code.. e.g. if you are writing a class and then write a class that consumes it your class is immediately available via intellisense. 

Extension methods need to be compiled before they show up in your Intellisense list.  So do not freak out or think the magic is gone.