does GUI affect battery life?
I think GNOME3 starts up using about 600MB of RAM, and LXDE starts up using about 200MB.
I guess that GNOME3 is a little more taxing on the processor, and maybe other parts, than LXDE is, as well.
Could this make a noticeable difference in battery life, for notebook computers?
It probably depends on what you're doing and what your battery is like. My guess is you won't be able to notice the difference unless one of the environments is using 3D acceleration (e.g. GNOME Shell, Unity, Compiz, Cinnamon).
I'd suggest doing some experimentation with the DEs you want to compare. Charge your laptop to full, note the time, and see how long the battery lasts, doing the kind of stuff you normally do.
According to these test the difference is not very big.
* http://www.phoronix.com/scan.php?page=article&item=uxklbuntu_power
* http://www.phoronix.com/scan.php?page=article&item=linux_desktop_vitals
Here's a few tips that could help too
Trisquel 6 32-bit uses 130MB with GNOME Fallback (default). 64-bit uses 280MB~300MB.
Cool, thanks for the information guys.