Comment 13 for bug 88152

I was having this problem as well with Feisty and nvidia geforce 6200. Tried both compiz and beryl and with nvidia-glx and nvidia-glx-new drivers and was always getting the black screen when changing back to an already logged in user. I also got this behavior whenever I ran a game that went to full screen and then exited that game. I tried chehov's fix above in beryl to no luck, then I also tried the following in the beryl-settings -> General Options -> General Options -> Main:

1. Uncheck 'Detect Refresh Rate'. The beryl wiki says that this does not always work and is not recommended, so not sure why it is selected by default.
2. Set 'Refresh Rate' slider to refresh rate being used by X.

After this I logged out restarted X and logged back in (simple beryl restart may be enough) and have had no black screens since then. I did a bunch of switching between three sepearte users and never had a problem. I didn't check to see if background users were using cpu up as chehov notes however, I will check into that.