It seems as much mumbo jumbo and tea leaf reading as it is the number on the casing of the tire. The number on the tire is typically a MAX inflation. But your weight, the type of riding, the brand and model of tire, how firm or soft you want the tire/ride to be, and the road conditions too all affect what you should run and there is no one 'right' answer.

With the same tire pressure, two different tires can give a very different ride. I used to run Vittoria Open Corsa CX 23c tires at 110, and the tires felt very hard and 'bouncy'. I had Vredstein Tricomps before and they felt a bit more plush at the same PSI. Now I have Continental GP4000 25c tires at the same 110 and they feel smooth and grippy, not bouncy, and just as 'fast'. If I ever get the Open Corsas again I will run them at 100 because they were so hard and unforgiving compared to the other two. But I am liking the gp4000s and will probably stick with them.

As far as flats go, it seems I get them more often as the tires get some miles under their belt.