Hello.
I was able to work my way out of this without having to reboot my computer, but thought I would report since this is the second instance of this behavior for me.
In short, I opened a new tab (You Tube) in an existing browser (FF) window, then my GUI visually scrambled and all local TTY's became unavailable. Other than the web browser, I had a pdf viewer (evince) and Eclipse open.
I was able to access my computer remotely and determined that lxde-binary was consuming 96% of the CPU. I was able to kill the process (sudo kill -9 [PID]) and start a new instance (sudo lxde-binary), after which I was returned to the login screen. I also had access local TTY's (e.g., CTRL-ALT F1-F6 on LM12 LXDE) again.
At any rate, like I wrote above, this is the second instance of this happening to me.
Any chance this is related to http://forum.lxde.org/viewtopic.php?f=8&t=31657 ?