There are many things to worry about in 2012.  The return of Quetzalcoatl, rampant earthquakes, flooding, other things that John Cusack is really good at running from.  According to NASA, however, solar flares are not one of them:

…[T]here simply isn’t enough energy in the sun to send a killer fireball 93 million miles to destroy Earth.

This is not to say that space weather can’t affect our planet. The explosive heat of a solar flare can’t make it all the way to our globe, but electromagnetic radiation and energetic particles certainly can. Solar flares can temporarily alter the upper atmosphere creating disruptions with signal transmission from, say, a GPS satellite to Earth causing it to be off by many yards. Another phenomenon produced by the sun could be even more disruptive. Known as a coronal mass ejection (CME), these solar explosions propel bursts of particles and electromagnetic fluctuations into Earth’s atmosphere. Those fluctuations could induce electric fluctuations at ground level that could blow out transformers in power grids. The CME’s particles can also collide with crucial electronics onboard a satellite and disrupt its systems.

via NASA