Recently there has been lot of talk about virtual goods which are sometimes referred also as microtransactions.

According to wikipedia definition:

Virtual goods are non-physical objects that are purchased for use in online communities or online games.[1] They have no intrinsic value and, by definition, are intangible.[1] Virtual goods include such things as digital gifts[2][3] and digital clothing for avatars.

Martin wrote recently here that
analysts estimate, this year, virtual goods revenue will be $1 billion in the U.S. and about $5 billion worldwide. Another analyst predicts annual revenues will reach $15 billion by 2012.
Not a small amount considering that they have no intrinsic value (beside online environment they are sold in). Most analyst agree that this is just a beginning  and that market is only starting to evolve into serious player in mobile services world.