At first, back when he did this in '94 or whenever it was, this was just slightly embarrassing and a little amusing. When he did it again back in May, it was slightly annoying and more than a little embarrassing but the amusement had ended. Now, after Camping has been told repeatedly by several different Christian leaders from several different denominations, this is beyond old and the annoyance has turned into a real problem but there's very little we can do about him other than combat his false teachings with the truth, which can be done by all parties without getting mired in deep Eschatological debate. I have to admit though that the Apostolic Churches have the upper hand here in that they could mete out Church discipline far easier than the Protestant Churches can. That's the down side of each Church being independent, doctrine cannot be easily enforced.
I don't think we can "do" anything about Harold Camping -- as I said it would be funny if not for the trouble he's causing people like here in this story.
One can only teach people and publicize it in the media that people should pray and live their lives like each day is their last.
Instead should publicise the right teachings (very difficult to get it on the media) and do damage-control, i.e. when the MSM goes overboard saying "look at what Christians believe", a Christian says "I'm Christian and I think Camping is a conman"