I have an Acer Aspire 5740-5780 laptop with ubuntu 11.10. I don't have the more common problem of the black screen on boot. Rather, under System Settings..., in Screen, under Brightness, with the "turn off after" set to x number of minutes, the screen will indeed turn off at the designated time, but the screen will not come back when I press a key. However, I am able to shut and re-open the lid, then the screen will recover. Any ideas on how to fix to this?
I suggest you try a screensaver that works, like xscreensver. I had that problem on a laptop, and after installing Xscreensaver and configuring a screen saver, everything went fine. You can find instruction on how to uninstall gnome screensver and install xscreensaver here
Also, don't forget what they say: Activate it in startup program. That way, you will ensure it is always on, and the screensaver is always running. Plus, a screensaver is more pretty than a black screen ^__^
I hope this will help you like it did for me