PayPal has released an update for its iPhone/iPod Touch that's indicative of how we may handle cash in the near future (though not exclusively with Apple products or PayPal, mind you): you can now "bump" money from your PayPal account into a friend's if they are close by.
Of course, nothing's stopping you from doing it the old fashioned way, which involves firing up the app and putting in a target email address. With the new update, however, it's much faster and it's a small but meaningful advance in how we deal with paperless transactions. Once you're close by to someone with the same setup, it's as easy as sending or requesting money at the touch of a button. The update also provides the ability to divvy up a single restaurant check amongst multiple PayPal users, which is where requesting money makes a little more sense.
Of course, your PayPal 2.0 mileage will vary, depending on how many people you know with an iPhone or iPod Touch and a PayPal account.