Docs for some of this still need to be finished up. Was planning on having this done already but got derailed by trying to get 7.3.2 ready.
The biggest thing is making sure that IPN is turned on in your paypal account:
1. Log in to your Business or Premier account in Paypal.
2. Click the Profile subtab.
3. In the Selling Preferences column, click the Instant Payment Notification Preferences
link.
4. Click the Edit button.
5. Select the checkbox to activate IPN.
6. In the Notification URL text box, you can either leave this blank or enter the url to the paypal-ipn script, ie.
http://www.ubbcentral.com/forums/ubbthreads.php?ubb=paypal_ipn7. Click the Save button.
At that point, it should just be a matter of setting up your group and subscription rates in the control panel.