I find the .NET anonymous type a bit weak in terms of a few more features:

1. Can't inherit/implement an existing type
   var x = new : IMyInterface {
      Number = 1,
      Name = "Hi",
   };
   
2. Can't add methods
   var x = new {
      Number = 1,
      Name = "Hi",
      Action = delegate(object o){ return true; },
   }

I guess anonymous types are purely for quick throw-away data constructs.  I might just as well write a class directly with all the stuff I wanted.