I'd just like to chime in here. I've been having these kinds of errors quite a bit nowadays. I've owned this phone for about a month and I would say this started occurring about a week. But to me, this problem manifests itself a bit differently sometimes. For example, sometimes, instead of just being extremely unresponsive (sometimes completely unresponsive), the phone will actually become hyper responsive to input or even act like I'm providing touch input, when I'm doing none. It's hard to accurately describe, but it makes using the Swype keyboard essentially impossible when it happens.
I'm running a custom rom, custom kernel, @ stock voltage & cpu frequency. However, seeing how this behavior persisted across several custom roms, I'm doubtful that it's really a problem with the roms. I do still plan to try a stock 4.0.2 rom. If anything, to get this phone replaced, it will need to be unrooted & with its bootloader locked.
Also, pressing the power button to try to escape the nonresponsiveness doesn't always help.