Many useful posts and articles about consuming or expose a REST service with BizTalk 2010, below the most important I found
Mikael Håkansson REST Adapter
there is other methods to consume a json REST service, with HTTP adapter and it is very simple, in this toy a sample.
This toy is composed by one orchestration that receive a fake xml message, a transform map to create a simple json string to test the call,
I used a flat file schema only to send a pure json string to adapter, just to make the test.
Naturally in real project we need to use a pipeline component to translate the xml message to json before to send the message to adapter and naturally vice versa.
To do this, the best way I know is http://json.codeplex.com/, this component is very well done and stable, but you can choose many different way.
Other important aspect is the setting of the port, no many parameters in HTTP adapter
Destination url, of the REST end point
Content type, naturally application/json
the toy is here
other toys in my SANDBOX here