I think bartering, trading items, and services like web design in exchange for a free advertising link on the top of popular site like Yahoo, YouTube, Google, etc may be a more popular form of payment rather than money since it is easier to trade something like a book or a service like graphic design of value instead of using money which is worth more or less depending on which country you live in like money from Mexico is worth a lot less than the US dollar when traded.
There are already sites like Craigslist which let users trade video games, comics, books, and goods and services as a form of payment.
It might work for physical produce like fruit which you grow yourself to trade for digital services like SEO, links, and graphic design could be worth it as long as the worker comes to your garden to pick up a few berries which he gets after he sent you his work via e-mail.
A lot of people also own physical products which are not worth much money like card board boxes, a used dictionary with a torn cover, etc and there are some people who might work online for physical products instead of paying money for your stuff because some people have no money to pay.
