Valve is planning to enter the hardware business according to a job listing on their website for an "industrial designer". In the posting Valve says "we're frustrated by the lack of innovation in the computer hardware space, so we're jumping in." While it doesn't mention what they plan to do specifically, it does seem that they will be going for something unique, "even in basic input, the keyboard and mouse, haven't really changed much in any meaningful way over the years... There’s a real void in the marketplace, and opportunities to create compelling user experiences are being overlooked."
Valve has previously said that they are building PC units to test Big Picture mode along with working on biometric experiments, however they said they were a long way from launching their own hardware. The company was either bluffing or things have changed pretty quickly.
Rumours also circulated the web over recent months indicating that Valve is indeed working on hardware. One rumour suggested that the company is working on a "Steam Box", a brand new gaming PC or console that would come with Valve's Steam gaming store fully integrated.