I did it with a 14" tv during a shoot where the talent could monitor themselves for a critcal take. The tv's color drastically changed in one of the corners after an hour... all green I think. After I returned the tv to upright position, everything went back to normal. I think the gases in the CRT didnt like that.
I can turn my JVC 9" over for about 20 minutes then I get a band of purple through the image vertically. When turns upright again nothing is worse for ware though.