I use AP regularly on I-95 around Boston and find it works 95%+ of the time where I drive. I have also used it on I-95 north to Portland, ME and as far south as Mystic, CT, and had no significant problems. I-90 and I-84 also mostly very good.
As for I-93, I have used it driving through Boston a few times, and agree that the lane markings are inadequate in some areas both north of the city and south. (I have not driven I-932 north of Medford, though.)