GDC: Valve confirms Portal 2
According to this, producer Kim Swift said in a G4TV interview yesterday, "Well, I believe Doug Lombardi who is our lead marketing director at Valve, has announced Portal 2."
Swift was probably referring to Valve's interview with Eurogamer a couple of weeks ago, in which Lombardi said we can expect to see "more Portal, for sure".
This is the first time anyone's actually mentioned "Portal 2" however. Teh internets, predictably, have gone bonkers for it.