There is a new page where all your circles are displayed and you can subscribe to some or all of them.
Word of warning!
Do not subscribe to all of them, as each post will create a notification under +Mr. Jingles and perhaps also send an email, depending on your settings. You will very soon be inundated in notifications! To undo the subscription you must visit each circle individually and click on the bell.
I recommend you choose carefully the people you place in a subscription circle. Keep it small.