There have been multiple books written about the pole shift phenomenon. I first heard about it as a young lad gobbling up science books. Geological researchers had found when sampling sea-floor deposits across the ocean that the magnetic alignment of atoms showed a pattern of geomagnetic field reversals. That the ocean floor had bands of material showing varying earth magnetic field alignments.
There is some alarmist thinking out there concerning the pole shift phenomenon. The greatly weakening magnetic fields is feeding a concern that the poles are due to shift in 2012. Why 2012? Ask the ancient Mayans and other cultures who drew up calendars that all end in 2012.
Anyway this article is a description, published through NASA, of current research and the current status. They say the magnetic field is indeed weakening, and that the earth is indeed long overdue for a magnetic field reversal. However while the field is weakening, it is far stronger than is typical. This means that if a pole reversal is induced by a weak magnetic field, the earth's magnetic field has a long way to go before it will happen. The article doesn't clearly say what scientists think causes field reversals, however.
