For the record, mandatory decryption is an unsettled issue in the U.S. and conflicting rulings have been issued. It's entirely possible that a judge in a given encryption case will rule that the accused's right not to self-incriminate as defined in the Fifth Amendment precludes mandatory decryption.

Regardless of the state's ability to compel decryption, you should still encrypt everything because it gives you at least partial control. Your options are much, much better if the government can't build their case without your cooperation, even if a judge compels decryption, because your lawyer can try to get the order rescinded before you comply, or at worst, he can at least stall for a while, you can claim you forgot your password and take the risk of an obstruction charge if the risk of said charge is lesser than the risk of charges that would be made after prosecutors gained access to your decrypted content, etc.

If you leave everything plaintext, you have no possibility of option or control; the government gets access to the whole kit and caboodle instantly.