AnandTech investigated the Intel 6-series SATA bug and learned that a faulty transistor in the chipset's 3Gbps PLL clocking tree is to blame for the issues. This transistor has a very thin gate oxide, which allows you to turn it on with a very low voltage, but unfortunately it appears an engineer did something without thinking and as a result the transistor is getting too high of a voltage, resulting in higher than expected leakage current. Over time, this leakage current can result in failure on the 3Gbps ports, but fortunately the 6Gbps ports are not affected as they're on a different clocking tree. Head over to AnandTech for some more details on how the situtation will be handled, it appears there won't be a general recall.
One fix for this type of a problem would be to scale down the voltage applied across the problematic transistor. In this case there’s a much simpler option. The source of the problem is actually not even a key part of the 6-series chipset design, it’s remnant of an earlier design that’s no longer needed. In our Sandy Bridge review I pointed out the fair amount of design reuse that was done in creating the 6-series chipset. The solution Intel has devised is to simply remove voltage to the transistor. The chip is functionally no different, but by permanently disabling the transistor the problem will never arise.
To make matters worse, the problem was inserted at the B-stepping of the 6-series chipsets. Earlier steppings (such as what we previewed last summer) didn’t have the problem. Unfortunately for Intel, only B-stepping chipsets shipped to customers. Since the fix involves cutting off voltage to a transistor it will be fixed with a new spin of metal and you’ll get a new associated stepping (presumably C-stepping?).