as I mostly shoot video, I have an LCD loupe nearly permanently attached to the LCD screen on my T2i, and hardly ever use the OVF (also, all my lenses except one are vintage manual, so I don't use any kind of AF)
once you get used to having all the goodies that an EVF has (in terms of information displayed alongside your image, and accessibility of the menus and options), it is hard to go back to an OVF, specially if it is a small one like the one on my T2i, or any other APS-C camera for that matter (with the louple, my "EVF" is significantly bigger than the OVF on a 5D2)
that's why I think EVF will be prevalent in the near future (given how well the new sony ones perform: resolutions seems to be no problem anymore, the only bit that still needs improvement seems to be the refresh rate)
the only bit that could be a bigger problem is AF, so I think in less than 5 years all manufacturers will go SLT for the high-end models and also some mid-end ones (some people need really fast AF, and/or will settle for nothing but the best) and mirrorless for everything else (as soon as contrast-detect AF becomes good enough for most)
@SLT: don't forget this is nothing new: Canon had SLT cameras in the 60s
http://en.wikipedia.org/wiki/Canon_Pellix)