I wouldn’t say the switching is completely inexplicable. People have done a decent job of modelling the dynamic processes that keep the Earth magnetic, including occasional reversals. By the way, I’ve heard that the signs indicate that the next reversal is coming in a few thousand years.
The consequences are not as dire as you fear. These events have happened many times without drastically wiping out life. Research is going on to see if the effects of the extra radiation have had a major impact on biology. Obviously, it would be a problem for people alive during the reversal.
A much more immediate problem arises from our own activities, which are already creating a huge "extinction event" of the sort seen every hundred million years or so, not the sort of piddling problem that may happen every hundred thousand years or so.
Assuming our descendants survive global warming, etc, then they probably will not have extraordinary problems with the extra radiation. Most of these charged particles (the only types deflected by the magnetic field) can be easily stopped by walls or even clothes.
Yes, in principle one can build a magnetically shielded house but it would be ungainly to say the least and really not worth the while since, as Mike hinted, the protons in the solar wind loose almost all of their energy traversing the earth's atmosphere.
A more dire circumstance would be if the earth's magnetic field did not reverse itself but simply died out to zero and stayed there. Then over the course of long time, millions or billions of years, the solar wind erodes the atmosphere. An example is the planet mars which has essentially zero magnetic field. The atmospheric pressure of mars is about one tenth that of the earth.
(published on 08/22/07)