Update : 07/10/13
So it would seem that the trademark information released last week may have been a hoax, which throws doubt onto the near release of Half Life 3, but there is good news! The info leak on the bug tracking software is still legitimate and this confirms fully what many people had already guessed; that Half Life 3 *is* being worked on by Valve, in the depths of the Valve HQ so all is not lost.
Valve has filed for a trademark on Half Life 3, the eagerly anticipated sequel to Half Life 2, which was released in 2007.
The trademark application is the cause for a build up of hype to resurface regarding the game. Gabe Newell and Valve in the past have been coy as to the development status of Half Life 3, in the hopes of not getting people overly excited to then not live up to hyped expectations. No other news has come out of Valve as to the game itself, so currently this application means little as Valve has as long as 5 years to use the trademark - but at least its a timeframe.
Valve also made a bit of a gaff when bug tracking software used by the company became accessible to public eyes, with one member of the Neogaf forums spotting a dev group titled "Half-Life 3 Core" and "Half-Life 3" under the service, the link to the bug tracker has now been removed. Will more details soon be available ?
To me this all seems to play towards the Steam Box, Valve could be taking pages from the console wars playbook where the main draw to each console was dependant on exclusive launch titles. I personally would hope this won't be the case. Hopefully all this commotion just means that we will be experiecing another amazing game from Valve, one that is in my opinion woefully overdue.