Although im not much of a beliver in the 2012-doomsday-scare myself, its funny to see some people here comment with absolute certainty on how the sun's gonna behave when the scientific community itself admits they really dont know much of how solar flares, or the sun for that matter, works in detail. There has been massive solar flares in earth's history that if it would hit todays hyper-electric society would cause some serious mayhem.
Will it hit in December 2012? Utterly most likely not, mis-interpreting the maya-calender in this aspect is a little like seeing the word "doom" behind your french toast and think that's a clear sign that France will cease to exist soon. Or a cheese doodle in the shape of Jesus and see it as a sign that his return is imminent.
And it also wont erase all data, or mean the end of the world. But one primary problem, I belive, is that it would fry power supply rather then information. Components in power plants that are really hard to replace would be destroyed if not they're not shut off in time, so my theory is that there'd be major power issues around the planet for some time, which could cause havoc.
But I think(but dont know) the chances for such a thing happening within our lifetime is fairly small. There's all kinds of bad stuff that could happen. Asteroids, Super Nova radiation, super-volcanoes, Iphones gaining self-awareness and going SKYNET on our arses.
All horrible but all very unlikely, except maybe the final example.
If one wants a likely "oh noes!"-scenario, look at global warming. Of course, global warming IS happening(despite what some really thick-headed oil executives are telling you), but at a much slower rate then these other more awesome "insta-kill" end-of-the-world scenarios. So maybe its not as interesting. Or as a certain scientist said: "Humans are built to react to imminent threats we can directly see. Threats that are on the horizon and are not directly visible, we dont care much about, generally."