This is a good question. Very small payments are problematic for other payment systems such as credit cards because they cannot scale as well as a P2P system. Especially when it comes to things worth a few pennies or less. In addition to requiring a profit, Mastercard must buy it's infrastructure and pay something additional to get anything done. Because of this, the micropayment economy may be relatively untapped.
I can envision a wide range of areas for such payments:
Internet advertising: those per-click based arrangements would automate well by paying in bitcoin.
Charitable giving: Tiny and anonymous contributions could be made directly to those in need.
Consumer promotional campaigns: Pay consumers , or charge for deals.
Small fair trade items: Doesn't get more fair than buying direct.
video game point system: Maybe you have the option to bet with your friends during a deathmatch.
Metered Internet services: Advanced searches, news, large automated services.
The big thing nobody saw coming:
