According to the Supreme Court of the Evergreen State (McKee v. AT&T, PDF)(via), it's unconscionable to use consumer contract language to specify binding arbitration in such a way as to vary from the state's prescribed class action rules, statute of limitations, restrictions on confidentiality, or availability of attorneys' fees. So it voided the relevant language in an AT&T consumer contract. To get to that point, it also voided a clause providing that the contract would be governed by New York law.
You still sometimes hear people describe the doctrine of unconscionability as if it banned mostly the sorts of contract clauses that no consumer would have entered knowingly or that no legislature would have prescribed as a reasonable balancing of the two sides' interests. In Washington, at least, the doctrine appears closer to serving as an all-purpose wrench with which the court pries off language in consumer contracts that vary from what it deems good public policy.