ValveTime.net has an image from a Valve Destinations-Importing Tutorial they explain shows that for about 24 hours an example screenshot showed a directory called Left4Dead3, taken as an indication that Valve may be working on a new installment in the co-op shooter franchise, which would mark the first time they'd managed a third installment in a series. The image has since been altered to hide that directory name, even though they note the original "leak" seemed deliberate. There are also some oddities about the amount of time spent in Left 4 Dead 2 by Tristan Reidford, the artist responsible for the leak that could also be taken as an indication that something is up here. Thanks GameSpot.