I’ve been making use of the JsonValueProviderFactory a lot lately. The JsonValueProviderFactory was released as part of MVC 3 and is a really easy way to introduce Json into your web application. In fact all MVC 3 websites support posting Json off the bat with no code changes. Phil Haack wrote an excellent blog post introducing the JsonValueProviderFactory.
One limitation I’ve found with the current JsonValueProviderFactory is when you have a property in your model that is a dynamic type. Unfortunately the JsonValueProviderFactory is unable to bind deserialized Json to a dynamic property. Example below: