Is there any evidence for a polar shift ever occurring?

Okay-this is something that people on Yahoo answers seldom admit. I am a Creationist. Anyway, I see all these people saying that every 300,000 or so years that there are polar shifts. Drastic calamitous polar shifts. First of all, these people never cite any evidence for there ever being such an event. Are these people pulling out numbers? I saw another guy saying that we ped through some black hole disc 3 million years ago. If most of this isn't exact science, how do they come up with these? Was this some Evolutionist convention coming together and making up numbers or do they get this due to current rates of polar shifting in the earth and current rates the earth moves. Second of all, wouldn't a calamitous polar shift that happens every 300,000 or so years completely contradict the idea that humans took millions of years to evolve? Where is the geological evidence for any such polar shift occuring?