I guess what really ruined me on it was the EOS-M that I bought not long after the 40. I can take it along with the 22mm in a package that's still very portable. Why take lens when I can have another camera and lens And for a bit more space, I can take the M + 18-55 IS and that covers a whole lot.
I bought a 35 f/2 IS a few months ago primarily to use along with my 70-200. It works great for this, but so does the EOS-M as you pointed out.
Two weeks ago our family spent the day at a theme park as part of a spring break vacation. I took most of my equipment on the trip, but accidentally left both of my spare batteries for my 6D at home. The 70-200 and 35 IS were my lenses of choice for a day in the theme park, but I was worried my battery in the 6D wouldn't make it all day. So, I opted to take my M +22/2 (and EOS adapter just in case) to use in conjunction with the 70-200 and leave the 35IS (and 24-70) locked in our vehicle trunk. This combination worked great! The 70-200 is a nearly perfect lens for theme parks with little ones, as you can get some terrific shots on the kiddie rides. It was also long enough to catch our older son and his buddy on roller coasters and more advanced rides. The M was perfect for the occasional wider group shot or in tighter quarters. The M is also a pretty effective video camera.
In the future I'll probably use the M in the role again (but will remember to bring my spare batteries!)