Frankly, I'm not at ease on this subject; I know the difference between a good (optical) viewfinder and a normal one, so I'm a bit skeptical about electronic viewfinders.
They have well known weak points, but also a very good strong point: the in-camera computer can alter the image at will, superimposing useful information, or even changing it completely.
And this is not entirely theoretical, as this article suggests:
The prototype 500mm f/4 G lens on show at the Sony stand at CES features a Direct Manual Focus (DMF) control that, when pressed, presents the user with a 15x magnified view of the scene to be photographed, to assist in ensuring focus is accurately placed. This is a feature that can only be possible in cameras designed with electronic viewfinders, so its incorporation in a professional lens such as this suggests that all future Sony Alpha cameras, including the replacement for the A900, with be designed as SLT models with electronic viewfinders.