Is Paypal considered a marketplace-style payment system? Two other newcomers are BalancedPayments.com (Gittip.com which has been getting some attention on HN i

Is Paypal considered a marketplace-style payment system? Two other newcomers are BalancedPayments.com (Gittip.com which has been getting some attention on HN is using them now) and BancBox.com . I have not used either but they are on a shortlist for a project I'm working on.