The popular indie documentary about indie game development will be the very first feature-length film to be made available on Steam. Indie Game: The Movie will be available on Steam June 12, but those who buy it early before its release can get a ten percent discount. According to filmmaker James Swirsky, the 1080p video "will be DRM'd as much as any other Steam product/game," which means you'll need to be running the steam client in order to watch it. As Polygon points out, this milestone for Steam could pave the way for other movies and non-gaming content to appear on Valve's popular platform, though the company has been selling PDF guides and editorial content here and there for quite some time.
You can pre-order Indie Game: The Movie via Steam right now.
On a semi-related note, one of my favorite games journalists, Gus Mastrapa, makes a cameo in the film. His column, Pretension +1 is one of my favorites because he talks about things that are interesting, like being naughty in Ultima Online. Old School.