As everyone else has already said, they're tiny and very easy to carry, especially if one is traveling and doesn't want to look like a tourist. There are drawbacks though, the built in viewfinders suck and loading isn't as easy as an M. They also tend to be a lot less expensive than M Leicas.
In 1970 I started traveling around India with two M4 bodies and four lenses. Found it to be too much gear and was worried about having things go missing. On follow up trips I switched to 3g or 3f cameras and worried a lot less. My first 3g only cost $125 and that included a 5cm Elmar. What I did miss was having some fast glass available, the 35mm Summilux on an M4 was great for available light.
Like a damn fool I sold my Barnacks quite a few years back, just keeping the M4s. Fortunately I realized my mistake and now have a very clean 3f with excellent glass.... 15mm CV, 35mm f/1.7 CV, and 90mm CV, plus a nice example of the old 3.5cm Summaron.
A Barnack is my favorite camera for concealed carry. Strap over left shoulder, worn under a light jacket just above the hipbone. It's very secure and can't fall off or be grabbed by a snatch and run thief. Only problem I've ever had was while getting patted down by airport security in Istanbul many years ago. The guard got a little freaked out when he thought I was packing heat. Fortunately no big problem and we both had a chuckle when I explained it was only my camera. After that I wore the camera around my neck while going through security.
Here's a link to another RFF thread where I uploaded a photo of 3f, M4, and D300 side by side. See message #18 ...
http://www.rangefinderforum.com/forums/showthread.php?t=57682&page=2 Which would you rather have hanging around your neck while using a squat style loo on an Indian train? Leaving expensive gear unattended at your seat is a good way to loose it, especially if traveling alone.
Glenn
