Both me and buddy experience this several times in different systems but never both of us at the same time. Because we could see the hud and had the mouse pointer, we just warped out and back in and we could see everything just fine.
I know you want more information, but forgot to make note of it and am at work right now but thought i should at least post this note. I know we both are running ATI cards, mine a 4850 and his a newer 6850. My drivers have been the same for likely a year already. His were newest available when he got the card less than a month ago.
Quick search of the forums didn't show this issue, but i don't like how the searches work so this might be mentioned all over the place and im not seeing it.
Will post more specific details later if warranted.