This was driving me crazy because I'm 100% a keyboard shortcuts person. After switching Spaces using the keyboard in Mac OS X Snow Leopard (I have my shortcuts set to *Control-Left Arrow* and *Control-Right Arrow*), my keyboard might stop working. I knew it was a software issue because I use [Teleport](http://abyssoft.com/software/teleport/) to control another machine from my main machine; during keyboard outages, if I moved the mouse over to the other machine, the keyboard would work over there. I did some Googling and discovered that it is the Dock process that is causing the problem. Go to **Applications->Utilities->Activity Monitor** (you'll have to use the mouse, unfortunately) and quit the "Dock" process. The Dock will relaunch itself and your keyboard will be working again.