OK, how many people have experienced this? If my Mac, recently installed with Mountain Lion, goes to sleep for an extended period of time (maybe hours rather than minutes), upon waking, everything hangs, freezes, whatever you want to call it. Beachballs over every app. Nothing responds, not even attempts to force-quit. It appears to be related to WiFi because it only seems to happen when, waking from sleep, the Airport icon in the menubar keeps searching but never connects (often ending up with the little exclamation mark icon inside it). This is a serious issue because it requires a forced shutdown (pressing and holding the power button), and that's never good for the OS. Even after that, on restart, I see the screen flickering, so I usually restart again and then everything's back to normal - until it happens again. At first I thought it only occurred when the Mac fell asleep on its own, and not when I sent it to sleep by way of option-command-eject, but sadly now I see that it happens in that scenario as well. One time it did this, I lost a password-protected Numbers spreadsheet forever, as it was open when the machine froze, and on restart it claimed it was missing the "index.xml" file - the document was no doubt corrupted when the machine froze. This kind of thing makes me feel that Mountain Lion wasn't really ready for release. Anyone else get this?