I have the GXR with M mount module and a Sony NEX-5n with the hawk's adapter, both cameras with their viewfinders. While the Sony EVF is nice, it has a higher pixel count, I don't mind the EVF on the GXR at all.
Both offer 100% coverage, which my lowly Canon's never do. And both also tilt for viewing at angles through 90° which makes shooting from a lower position done more easily.
And I really prefer the camera body in every way to the Sony. The GXR has more buttons, but they are laid out intelligently and you can assign a lot of functions to them. I've customized the buttons to allow me to change metering pattern, ISO, exposure compensation and start MF assist - all without having to go to a menu setting! And with a dial, I've input 3 lenses to provide for EXIF info for them as well as change the defaults - I mirrored my settings across all lenses, but you could have different metering pattern, exposure, image type etc with the turning of a dial.
Perhaps the most surprising is that I use the live view screens half the time, which I've never done with digital cameras before. These 3" ground glass-like viewports make excellent finders too! And the sony, with it's tiltable screen is nice!
Is any EVF as clear as an optical? well of course not. But with the advantages of focus assist and two different sizes (EVF and live view screen) I can't say that they are worse than on optical VF and for how I use them, often better.