Thus far payments on Facebook and MySpace are largely limited to payment for applications. Over at TechCrunch Michael Arrington weighs in on the lack of micropayments:
Today app developers on Facebook and MySpace can create revenue by
showing advertisements at very low CPMs. On the iPhone/iPod, developers
can also charge for applications at the time of sale.
Both of these are great ways to make some money on software. But the
third leg of the stool, micropayments for things like virtual gifts and
other things, has been largely ignored to date.
There are Facebook applications that have found a way around the
problem by using third party payment services. Spare Change (powered by
PayPal), Social Gold, Zong and other services let users move cash into
the system, and applications like Mob Wars have gathered as much as $1 million per month from micropayments.
Arrington goes on to predict that Facebook and MySpace are likely to partner with third parties (why replicate PayPal?) but that Apple will continue to create it's own solutions (not surprisingly).