CAIR Oklahoma claims in their "Understanding Sharia" brochure that it, "sharia," has historically been allowed in American courts. If this is true, it's news to me! I'd like to see a listing of the court cases where this happened, wouldn't you?
For clarification, as I understand it, sharia is religious guidance for Muslims while sharia law is Islamic jurisprudence.
Update 12/16/11: Florida judge backs off decision to use Sharia Law in mosque lawsuit
Below is a copy of their "Sharia" brochure: