Reports are that Apple CEO Tim Cook was seen at Valve Corporation's headquarters in Bellevue, Washington. It is unknown what the visit pertained to, though a personal visit from the Apple CEO is somewhat significant in and of itself - this wasn't just a biz dev guy.
Since the launch of the App Store in early 2008, games have become a more important part of Apple's overall revenue stream. Apple's Game Center was a clear demonstration that the company takes games more seriously, and it is scheduled to release on Mac OS X Mountain Lion in Summer 2012.
Valve's Steam is something like a counterpart to the App Store, although its focus is purely on games and not general purpose apps. Steam has run on Macs since 2010.