Yes, good money can actually be made in the rapidly-growing world of free-to-play massive multiplayer online games (MMOs), but just how much can micro-transactions actually generate? Unfortunately, average revenue per user information is often concealed behind the fog of competition by privately held game makers reluctant to report either very high or very low results.
To add to the confusion, some developers choose to report their "average revenue per paying user" (ARPPU) which, by definition, is always more impressive than their "average revenue per user" (ARPU). (Both of these statistics relate to monthly logged-in users, and the amount of monthly logged-in users cited in ARPU is often a fraction of total registered users -- a common metric used in press releases.)
The inability to get at the real "metrics-to-success" can make it extremely difficult for a developer mulling whether or not to enter the free-to-play MMO sector.