Don’t jump off your seat in excitement as it can mean anything. It’s true that @Ekanaut, the marketing guy at Monday Night Combat dev UberEnt found one of the Valve Employee wearing a Half Life t-shirt but this does not mean that Half Life 3 is near.
I am not saying that Half Life 3 isn’t coming, it’s just that Valve is taking awful long time for the much-anticipated sequel. As far as the t-shirt is concerned, I can make something like that (being a fan) for Half Life 4.
The only hope we have is that since the shirt was on the body of Valve’s employee, they are on the move and we might hear about the sequel soon!
Come on Valve, Tell us already!