Personally, I haven't felt the difference between the Oly EVF and the Sony EVF. Tested a friend's Nex. They may be very slight. The difference between either of this and my G1's EVF, however, is huge... Lots of 'tearing'...
Don't find alot of difference b/w nex5N evf and pen vf2 in terms of resolution although on specs it is huge. The difference though is the focus peaking which is especially useful for manual lenses.
I switched from 60D to E-M5. The EVF is very different from an OVF, especially under difficult lighting. This is because the EVF depends on the sensor, which has limited dynamic range. In fact, the EVF will show high ISO noise under low light conditions because the sensor has to increase its sensitivity so that it can maintain the 60Hz refresh rate of the EVF (equivalent to taking 60x 1/60s shots every second). This is when an OVF, which is only limited by the sensitivity of your own eyes, shines.
Of course, the actual photo will not show the same noise if you mount the camera on a tripod and use a longer exposure to compensate for lower ISO (which is what I would do). But it is quite unsettling to see all the chroma noise in the EVF when you are composing the shot. The colour dots can also be distracting and make composition difficult.
I find it acceptable because I have grown accustomed to EVFs after using a Panasonic FZ18 (superzoom camera with EVF) for a few years before getting my 60D. But it can be limiting for some people.
Ya, EVF can be limiting for long exposure shooters using ND filter. For the most part it's acceptable, especially so for manual focusing and bright day light. Otoh, it can be very useful like ability to magnify which OVF certainly can't, in situations like macro, and manual focus.