My Mechatronics unit was replaced under warranty on my first DSG and was fine afterwards, but the other two cars I've had have both been excellent. I haven't heard of any recalls in the UK, but the USA have had a faulty batch with failing MCU's, which prompted VW to up the warranty on the DSG box in the USA to 10years. So far this hasn't been extended to anywhere else AFAIK. 99% of DSG cars in the UK that had this fault will have had the MCU replaced if it was faulty under warranty as it is noticeable.
Some obvious symptoms are.....
Jerking into gears on accelleration and decelleration
"Kangarooing" at low speeds up to approx 30mph
Lack of control in reverse - the car surges and again clunks into reverse.
Uneven "lumpy" idle.
Extreme symptom is stalling from standstill
Some of these symptoms (2 & 4) could also be from a failing/failed coilpack.
Reasonably speaking though, there are an awful lot of DSG cars out there and it only needs relatively few failures to highlight issues, especially given the potential expense of a new MCU or gearbox. The boxes are a lot stronger than people think - just look at what I've been pushing through mine for the last 18months. If I had a manual gearbox I'd be at least on an aftermarket clutch by now....and those cost upwards of £500!!
Sleep tight guys and don't have nightmares