Well, draugnar, it seems to me that to say, "all predictions have failed, therefore AGW is ridiculous" is a bad oversimplification.
First, I have to assume that you are correct when you say, "all predictions have failed." Let's accept that at face value, for arguments sake (I am not yet convinced that this is the case, but it's not germane to my reply so who cares).
The second assumption we have to make is that an untrue conclusion means that the premise is untrue. By way of example, if I say, "Gay marriage is now legal, therefore the world will explode in the next ten years." Tick-tock-tick-tock 10 years later, but the world has not exploded! Does this prove that gay marriage is not legal? Clearly not. All it proves is that somewhere along the line a mistake was made on the way to my conclusion.
So even if it is true that, "no predictions have come true," that allows one to conclude precisely nothing about the truth of AGW (for or against). It only allows one to conclude that the specific hypotheses (AGW will cause A, B, and C) are likely untrue.