Beth, I agree wholeheartedly with checking your accounts online constantly. I also had problems with the credit union depositing a check to my savings account instead of my checking and then bouncing checks. I chewed them out seriously.
Had another case when they called me about my late mortgage payment. I told them I not only had sent the check in (I was not using electronic payment then) but that they had cashed it! They had deposited it also but did not credit it to the mortgage.
I check it a couple of times a week--probably once a week is enough.