I know the idea of hacking various MF lenses onto the camera is appealing to gadget fiends, macro enthusiasts, live view fans, and people who always wanted 114mm f/1.2 lenses, but outside of that, the resulting package is as big, as heavy, and more clumsy in most cases than using bodies that took the MF lenses in the first place.
Well. no. I put Leica lenses on my E-P1, and the package is smaller, since the E-P1 is smaller than a Leica body in all three dimensions. And notably lighter. Also, some Leica lenses (the Nocti, and anything longer than a 75) can be troublesome to focus. No problem with an E-P1 -- I can focus more quickly and more accurately with the longer lenses than I can with an M8. And it's interesting to use a 270-equiv in Leica glass, with IS.
I have both the E-P1 and the G1 (one as the backup for the other) and the G1 is, I think, a better camera -- but there are uses for the E-P1, and though I also believed that a viewfinder was pretty important, I'm finding that I can adjust just fine to the LCD finder. I don't hold the camera at arm's length, either, although I'm 65 and suffer from the usual old-guy eye problem. But I find that if I brace both elbows on the sides of my body, in a posture not much different than I use for the M8, with the LCD 10 inches to a foot from my face, I can focus just fine. The bigger problem is that with a viewfinder, in many ways you never stop looking at the subject -- you simply move the camera in front of an eye. With the LCD, you actually have to look away from the subject, and since your hands may not be pointing in the exact same direction as your eyes, you may have to move it a bit to find the subject...although this problem tends to go away with practice.
I travel quite a lot, and these cameras are a great benefit - not only the body sizes, but the lens sizes, as well. When I get the 7-14 Panasonic, which is supposed to be delivered later this week, I will be able to cover the equivalent of 14-400 with three lenses, with image quality good enough for most ordinary print media (mass circulation magazines and newspapers). And the travel package, with two bodies, will fit in a regular carry-on travel briefcase *with all my other travel stuff.* It is *substantially* more compact than a Leica kit of two bodies and four lenses, and much lighter. The IQ is not as good as with an M8,, but for most of my purposes, good enough.
JC