this is my first post - I've not been able to find any other people with the same problem!
I'm using Lubuntu 12.04 on an Acer AspireOne Happy2 netbook (Intel Atom n570) having grown quite frustrated with the slow responsiveness of unity on my computer.
I've used the power manager to set my screen to dim on battery after 30 seconds (and tried 10, 60, etc etc) but it won't do anything. I really want to use this setting as I use by netbook on the go a lot and will get a fair power saving out of it.
Could there be conflict stopping this from working? I've tried lots of tests and options, with no joy.
(7/5/12 edit) Thank you very much for your advice - I've removed xscreensaver, but unfortunately it hasn't fixed the problem. I can adjust the brightness using the system keys on my keyboard, so I can rule out a problem with the brightness control. I think it might be the interaction between the power-manager and the screen brightness controller.