I've had mine for 2 weeks or so and it's been fine. Once it took a long time to wake up, but no serious issues.
Well, there are two.
When the Pro sleeps, it produces a high pitched but barely noticeable buzzing noise. It's cyclical and it's completely quiet in between cycles. The frequency is maybe every 5-6 seconds. I'm not sure what it is, but I haven't made a serious effort to look yet. The only problem is that the computer is in my bedroom and it's an annoying enough noise that I can't sleep with it on. Meaning if the Pro sleeps, I don't! Anybody have any ideas? My next step is to open it up and press down on various things as it's sleeping. Not that excited to do that with the power on though....
The second issue, I've found that I like the keyboard a whole lot. I'm typing the fastest I ever have with it. The mighty mouse is another thing though. I love the functionality of it, I think the scroll wheel is great. The ergonomics though, are terrible. The mouse has no support for your hand at all, essentially either you keep your hand in the air and your arm gets tired, or you rest your hypothenar eminence (pinky side of your palm) on the mousepad. It all seems like a setup for some sort of repetitive motion injury.
Otherwise, no major issues and love the computer and the 30" ACD.