Are Bad RAM Chips Common?

A semi-Anonymous Coward asks: "I recently built myself a new system using a mainboard which required using registered DDR SDRAM -- the motherboard will not work with unbuffered / unregistered memory, and I wanted the extra integrity provided by registered memory anyway. To my amazement, both the memory I purchased with the board and one of two other sticks I purchased were either defective or simply incapable of working with the board (which is the Chaintech 7KDD, BTW). About how often do people run into defective memory, and do they see them from the 'reputable' manufacturers as often as they do the 'no-name' ones? Now that I've spent a ridiculous amount of money on this, I'm a lot more wary."