There were no difficult algorithmic questions. If you know your basics on algorithms and data structures you should be fine (I was asked a tree questions, and array pattern search question). I interviewed for a position in mobile sdk dev so the interviews focused mainly on architecture and design. Practice your object oriented design, and think of how to design things to securely and to scale (client/server side caching, security, etc.). These questions can be particularly tricky for someone coming right out of college. Also, Paypal values a good culture fit so be enthusiastic, sociable, and confident.