It certainly happens from time to time. There are few gross effects, and in the past, when no one knew about them the most drastic results were spectacular aurorae, still unexplained in those days. Biological threats in past times were trivial, and in my opinion they will remain so even if our magnetosphere collapses.

As for how to predict them, I do not know any means that might be more effective than establishing a few suitably placed and equipped satellites to detect the processes producing the ejections, and the events of their being launched in our direction. The fact that we do not have a few such satellites in action at least at our L1, L4 and L5 points, if not at say, the orbit of Mercury, I regard as typical of the disastrous effects of the scientific illiteracy of politicians.

The trouble is that while our understanding of solar and planetary physics has grown, our vulnerability has grown a good deal faster. Something that coronal ejections definitely can cause is disastrous voltage surges in our major electric reticulations and some other electircal installations as well, even in some of our satellites.

If we don't get some sort of effective measures in place pretty soon, we are laying ourselves open to something that might make the boxing day tsunami plus the sub-prime bubble look like a passing fuss in the kiddies pool.