Double-opt-in not working. Should have the option to single-opt-in or confirm-opt-in anyway

According to CRM-2861 when a user signs up via a profile to a mailing list group and CiviMail is enabled, they will be added to the group with a pending status until they click the confirm link in a confirmation email. This is not happening (confirmed on 2.1 demo site). The contact is added to the group with the confirmed status (i.e. there's no difference between mailing groups and non-mailing groups).

However this brings up the point that double-opt-in isn't required by law. There are rumors that some ISPs require it, however I can't find any official documentation stating such, nor can I see it being feasible to monitor.

I am working with a client who would prefer confirm-opt-in (the contact receives an email stating "You have signed up for our newsletter, if this was an error click here to unsubscribe"), with no double-opt-in verification link. This is certainly simple enough to do with form hooks. But if double-opt-in all of a sudden starts working, I'll need to find a way to turn it off.

Perhaps the group settings form should have options to choose single-opt-in, confirm-opt-in, or double-opt-in for mailing-list groups.