I have experienced the following issue. This occurred after upgrading from 11.04 to 11.10.
I have an intel graphics card, as confirmed by the command:
ari@ari-laptop:~$ lspci | grep VGA 00:02.0 VGA compatible controller: Intel Corporation 2nd Generation Core Processor Family Integrated Graphics Controller (rev 09)
There are no proprietary drivers on my laptop.
When I leave my laptop inactive for more than a short period of time, so that the screen lock activates itself, it is frequently impossible to reactivate the screen. It "comes alive" with a faint grey hue that fades to black within a few seconds and nothing shows up no matter what action I take. The only solution is to turn off the laptop by pressing power on/off for a few seconds and then restart.
Interestingly, when I have an external monitor attached the issue persists on the laptop screen, but the external monitor remains active and functioning.
The consequence is that I have to reboot my laptop several times a day.