Microsoft has released an article and sample for consuming RESTful services from BizTalk. This is a good treatment of the topic, a topic which has been inadequate until now.

Article: http://social.technet.microsoft.com/wiki/contents/articles/invoking-restful-web-services-with-biztalk-server-2010.aspx

Sample: http://code.msdn.microsoft.com/Invoking-ReSTful-Web-with-776ceb78 

Good stuff!!