Looks like American Express' answer to Paypal/Amazon Payments/Google Checkout (and to a lesser extent, Square) and allows free person-to-person transfers.
Sending
It's as easy as e-mail. In fact, it is e-mail. Just send money via your Serve account to the recipient's e-mail address.** Once they've confirmed the transfer, your payment is complete and they're paid in full.
Receiving
Anyone with a Serve account can pay you quickly and easily by sending funds to your email address. If you're already a registered Serve user, you simply accept the transfer and the funds will be deposited into your Serve account. If you're not yet a Serve customer, your notification email will take you through the easy registration process.
Before June 12, 2012 there is also no fee for funding serve via credit card (2.9% + $0.30 after) but could this be a way for you to hit minimum spend on credit cards before then? They also send you a physical serve card that can be used at merchants and ATM... so ideally you could just load minimum spend onto your serve.com account before June 12 and get the points for no fees, then use the serve.com card to buy stuff. Or am I missing something here?
http://www.serve.com/