ZapperZ's article is very comprehensive as far as what it covers, but I don't think it addresses the OP's main question, which is about the chance of success in finding a permanent job.
If you get a PhD in physics and are good at what you do, then you have basically a 0% chance of being unemployed. However, you do have a significant change of ending up in a job that didn't actually require a PhD in physics, and your chances of finding a job doing research are very small. This is just a matter of statistics. One person doing physics research will typically produce some large number of grad students over the course of his/her career -- say 10. The number of physics jobs doesn't grow at an exponential rate of anything like a factor of 10 per generation.