I personally think it is in an underdeveloped state and shouldn't be used until at least the next major release.
In the mean time, try paypal subscriptions. Billing is automatic, credit card processing is secure, and you don't run the risk of having someone steal your customers personal information off your server, which you would be liable for if it happened.
If you have already gone throught the trouble of getting a merchant account with someone like authorize.net or linkpoint central, they too can auto process against your customers card each month, for a fair monthly fee. This also relieves you of the burdon of securing your customers most private information.