arrived on Steam including Global Agenda and Champions Online. The micro-transactions within the games will all be available through Steamworks (to my understanding). Anyone familiar with buying hats in Team Fortress 2 will understand the Steam integration of micro-transactions.
This is really good news and Steam is a perfect vehicle for F2P games. The biggest barrier to subscription games is requiring a credit card up front. F2P removes that barrier and then the biggest barrier for F2P games is the client download and account setup. Both of these, for the most part, can be taken care of via Steam.
I'm looking forward to more F2P games to hit Steam. Personally, I'd love to see League of Legends or Allods Online on Steam. Of the first wave of F2P games, I may try out Forsaken World (a straight up WoWDiku MMOG) or maybe Spiral Knights (co-op dungeon beat'em'up) or Global Agenda (shoot em up MMO thingy).