A job posting from Valve has sparked new speculation that the developer might be bringing their popular Steam service and library of Source engine games to Linux.
The listing, for a Senior Software Engineer, states that one of the position's responsibilities will be to "port Windows-based games to the Linux platform." As Valve's games are exclusively available through their Steam storefront, the logical conclusion is that Valve is planning to bring the entire service to Linux at some point in the near future.
There were similar rumors at the end of 2010, when the company announced that they were porting the Source engine to Max OSX. The rationale was that the developer had already cleared the biggest hurdle in offering Linux support by implementing support for OpenGL rendering, and getting the Steam client up and running would be a fairly trivial step by comparison.
Of course, that never came to pass, but all the reasons that made it likely back then are just as true today, and this job posting are evidence that, at the very least, Valve's giving the topic some serious consideration.