Building a ToJSON() Extension Method using .NET 3.5

Scott Guthrie has a good article on his blog about building a ToJSON() Extension Method using .NET 3.5

Extension methods allow developers to add new methods to the public contract of an existing CLR type, without having to sub-class it or recompile the original type. In doing so they enable a variety of useful scenarios (including LINQ). They also provide a really convenient way to add a dash of "syntactic sugar" into your code.

Read the complete article here:
http://weblogs.asp.net/scottgu/archive/2007/10/01/tip-trick-building-a-tojson-extension-method-using-net-3-5.aspx