I figured it wouldn't take long for Oly Pen fans to speak up. Interfaces are funny that way, everyone has a preference and nobody is wrong. What works best for you is really all that matters. And, like KEH said, sometimes other factors are more important.
Just to be clear, my biggest issue with the Oly MF interface isn't toggling the magnified view on/off, which is pretty easy. What bothers me most is having to toggle through display modes to adjust ISO/WB when using mag view.
I change the ISO often. Especially w/mf lenses, I'm often indoors, with the lens wide open, and changing ISO is the only way to maintain shutter speed. Subject is near a lamp, ISO 400 works OK. Subject moves away from lamp, gotta bump up ISO to 1200. Have to refocus after subject moves away from lamp.
With my E-P1, I have to hit Info, adjust ISO, hit Info, hit OK to magnify. If the subject moves back near the lamp, you gotta do it all over again. It's tolerable for me because I only have two display modes active. If you want to keep some other display modes active, you have to hit the Info button many more times.
The G1 toggles mag view off with the shutter release, which I find more intuitive, or pushing the Menu/Set button. It is much quicker and easier to exit mag view to adjust ISO/WB, then jump back to mag view.
For me. YMMV.....