Does PayPal integration work right-out-of-the-box?
Yes, it can even generate your PayPal® Subscription Buttons for you. Everything is fully integrated. You even get to create your own Pages within WordPress® to handle Membership Options, the Login Welcome Page, etc. For advanced webmasters, there are scripting techniques that are documented as well. These will help you further develop your site and tailor it to meet your specific needs. s2Member API Scripting is NOT required however.