I must admit, that I am guilty of being a double-spacer. Your argument and sources however seem to be sound, so I think I shall give a go at doing it the correct way from now on. I've been becoming more and more interested in typography lately, so let's bring this movement to the forefront and starting single spacing after punctuation again!

(Notice: The double-space has been so ingrained in my typing for so many years, I even did it in this comment without even realizing it!)