The advantages of an optical viewfinder are obvious, especially in fullframe. You see what you get instantly, no delays. On the other hand EVF's score some good points also. Especially for smaller formats than fullframe. They offer 100% coverage of the picture, they show immediately the effect of corrections on exposure, they compensate for low light or slow lenses through the gain of the EVF, they're way better for manual focus if you can magnify the viewfinder and last but not least you can judge the pictures you took in the viewfinder even in bright sunlight. A lot of advantages and I probably forgot a few. But there's this one nagging disadvantage. The time lag, or the blur as it shows in the A99.
But this has become better in the last few years, resulting in only a slight blur in Sony's A99. I guess that in a few years the refresh rate of an EVF will be higher than the eye can detect. That's the day the EVF meets an optical finder. Will it replace optics? Time will tell, but EVF's are here to stay and will conquer SLR terrain more and more.