This excerpt taken from the EBAY 10-K filed Feb 17, 2010.
PayPal offers three types of accounts: Personal, Business and Premier. A new account holder typically opens an account to send money for an eBay purchase or a purchase on another website, a payment for services rendered, or a payment to an individual in lieu of cash or check. Allowing new account holders to join the network when they make or receive payments encourages PayPals natural, user-driven growth. PayPals account sign-up process asks each new account holder to provide PayPal with his or her name, street address, phone number and email address. The account holders email address serves as the unique account identifier. PayPal also offers certain customers who sell on their own websites the ability to accept credit card payments from buyers without requiring the buyer to open a PayPal account.