"It's worth noting that in my testing, GNOME uses slightly more RAM and CPU than Unity on the same hardware doing the same things. The increase is only about 10 percent more on the RAM, and, let's face it, neither of them are lightweight desktops. If you want something light, try i3."

Best advice in the article ;) I did try i3 and like it a lot. I have it running on a Chromebook now as my main machine.