The shifting of the magnetic poles are indeed caused by electrical currents running throuh Earth's outer core and lower mantle. These currents fluctuate probably due to the sloshing of the mantle.
A potentially serious concern, especially for aircraft navigation systems, is that we are overdue for another magnetic field reversal(in terms of strength and direction of current), as the magnetic field has been switching every 700,000 years for last 2-3 million years. There is an awful lot of evidence of reversals, especially in volcanic rocks, which contain iron deposits.
Currently, the north magnetic pole is stronger than the south magnetic pole(sitting in Antarctica). A reversal would be a problem because during that time, the magnetic field is temporarily weakened greatly and compasses or navigational aids that rely on compasses would be rendered useless worldwide. Aircraft, both commercial and military, rely on navigation systems greatly. This will be a problem, unless a greater emphasis is placed on satellite navigation systems, like the GPS. The GPS(Global Positioning System) is a network of at least 22 satellites currently in orbit worldwide. If a commercial aircraft used this, only 3 or 4 satellites are used to triangulate the position, which is accurate within 100 metres(330 ft). The military version is about 10 times more accurate.
Also, with the magnetic field weakened during a reversal, there is the concern of greater exposure to cosmic radiation and charged particles from the sun at higher altitudes, not only to astronauts, but also pilots and passengers who fly frequently enough. Although the greater exposure wouldn't be that deadly, cancer is more of a problem. Even now, the region around the North Magnetic pole is a concern to such people on polar routes, because there is less of the magnetic field protecting Earth from the cosmic radiation.
A reversal would probably take about a century or perhaps over a thousand years, but little is known about them, as a reversal has never happened in recorded history.