I've used Goo-Gone on plastic before. It's not bad. What I got yesterday was in a spray bottle. I just sprayed it on, let it sit a minute or two, then wiped it off with a paper towel. I had mixed results. some of the scuffed-on paint and stuff came off, but a lot of it stayed put.
I'm going to put the G5 through its paces vacuuming the living room and master bedroom when I get home from work this afternoon.