This is the second time this has happened, both times being when I'm in the middle of a lot of work with several things open and it's really really annoying. Out of nowhere, Expose, Dashboard, and Command-tab have all ceased to work. The only way I can switch windows is using the dock in combination with the Window menu in each app. Not only that, but my keyboard shortcuts for QuickSilver (and all triggers I've setup in QuickSilver, like for iTunes) also cease to work. I quit a couple apps, and quit and restarted QuickSilver, but to no avail. This is probably the most irritating bug in OS X I've come across. I really don't want to reboot to fix this. Does anyone know what causes this or how to fix it? EDIT: And now, a few minutes later, it's working again. I didn't do anything, didn't open or close any apps.