I'm sure Arda mentioned this in chat, and it was mentioned in the site too, but for the life of me I wasted 15 minutes trying to get back into TF2 after alt-tabbing out, then wasted 15 minutes trying to find the relevant piece of information again.
So I'll ask: how do you turn "fake fullscreen" (windowed mode maximized without border) in TF2, L4D, HL2 and the other Source games?