Yes I have painted many airplanes over the years, both open bay, and fully sheeted. Here are a couple of pictures of painted 40% airplanes from years ago, and one that is Monokoted three years ago that I still fly today, it is the red and black 40% Carden Extra 260, it has over 500 flights on it, and weighs 28 lbs. with a DA 100. Both of the painted aircraft had almost 4 lbs. of glass, covering, and paint on them, but I figured if I was going to paint these, then they were going to have a finish of a show car, and the hell with the performance. I am happy to say I don't think that way any more, and have tought myself to cover in Monokote with a finish that will stand up to any painted airplane in looks.

Here is a short video of what you can do with a really light 40% airplane on a 100cc engine.
http://icanflyrc.com/JRFlyin/slides/Bob260.html

Bob