It is extremely unlikely anything will happen. Every single generation insists that it's only a couple of years or months until Jesus comes back. So far, they've all been wrong, and I see no evidence that this Camping fellow is any less wrong. As stated before, all he's done has been to create some crazy calculations, based on nonsense, that state that the world will end on the 21st of May.
You know those old homeless, mentally ill people who stand on street-corners saying "The end is nigh, the end is nigh"? You don't pay attention to them do you? Well, why would you start paying attention to them if they started putting up billboards? If I could draw an editorial cartoon, I would have the first panel depicting a homeless man holding a sign saying "the end is near", with the caption "Crazy Man", and the second panel will be harold camping holding up a sign 50x larger saying "The end is nigh", and the media swarming about him with the caption "Media sensation!". Because that's how I see it - the only difference between Camping and the old bearded homeless street-corner prophet is the size of his sign.
We shouldn't pay any attention to him. He's been wrong before (he predicted the world would end in 1994), and he's almost certainly wrong this time. I'm not a religious person, but even the religious people I know write him off as a complete loony.
