MBP (running Lion) frequently hangs, needs restart

Since I bought my Retina MBP last fall, it's had a habit of hanging and needing to be manually restarted.

It will start with whichever application I'm in (usually Chrome) not doing anything new, e.g., Chrome not loading a page when I click a bookmark or type in an address, or another application just hanging.

Activity monitor won't open, force quit has no effect, and every app turns out to have the same problem. The only solution I've found is to manually shut down the computer using the power button, and turn it back on.

Sometimes it doesn't happen for weeks, and sometimes (like now) it will happen once or twice a day for a while. Because it's so unpredictable, I haven't been able to do much testing, like shutting down certain apps and seeing what happens.

I think there must be system logs or crash logs somewhere. When I turn my computer back on, it recognizes that I shut it down due to "a problem" (when it offers to re-open my applications), so I'd imagine somewhere it keeps a record of what went wrong. Would that be of any use in diagnosing the problem?