A bug that slipped through our QA testing is causing AdBlock 3.0 not to save your setting for Acceptable Ads (AKA Allow some non-intrusive advertising in AdBlock's options, GENERAL tab). This makes it impossible to disable the option. We're sorry about that!
A fix is under review now and should be released by tomorrow. In the meantime, there is a workaround! Just go to the FILTER LISTS tab and disable the Acceptable Ads filter list directly.