I hope someone is still listening to this thread. I bought a 2011 SL that has 8,500 miles two weeks ago. It was fine for about four days and then while driving it, the screen went black. I punched the day/night switch to no avail, and eventually came back on by itself. Then it would switch from working (the screen and buttons) to not working. The map continued to move as we drove, but the system wouldn't respond to any buttons, either on the dash or steering wheel. And then it would start working again.
Took it to the dealer - and naturally - for two days it performed flawlessly. I picked it up, drove it home and then went out to meet a friend for lunch - and it screwed up royally, restarting, blacking out, responding and then not responding to buttons. The ultimate irony? The service manager tried to call me back while I was driving - and I couldn't answer the call because the screen was not responding to touch commands.
So, I just checked the 12 volt battery. 12.16 volts with the car off, 11.78 with the car on. Sounds to me like that's not good, so I'm going to replace the battery tomorrow and see what happens.
From what I've read on the site, no one has had this kind of erratic behavior - but if you have and are reading this, absolutely let me know what fixed it if one exists. I've been told the replacement part is $6k, which is more than I paid for the trade-in to get the car. I love the car in general, but I sure picked a lemon, it seems.