Once you start thinking of your object model as data, you can do amazing things. Want to find all the types in your system that implement an interface and spin them up?

     var rules = 
		AppDomain.CurrentDomain.GetAssemblies
		.SelectMany(a => a.GetTypes())
   		.Where(t => typeof(ISecurityRule).IsAssignableFrom(t))
   		.Select(t => Activator.CreateInstance() as ISecurityRule)
   		.OrderBy(r => r.Priority);

You can then run a chain of responsibility by writing

    var allowed = rules.First(r => r.Check(someObject) != null);  
    //Check returns null when a rule isn't relevant to the object being checked

it's pretty sweet for metaprogramming when you can run queries against your codebase