I have an E-M5 and used to have a T3i. Jpegs from the T3i had a slight softness to them that was a big turn off. Also wierd jpeg colors from time to time that no amount of white balance tweaking could fix.
From carefully studying camera review site sample photos, I bought an Oly E-PL1 as an experiment (a mere $280 with kit lens on Amazon). I was blown away by how superior the E-PL1's jpegs were compared to the T3i's in image detail resolution, sharpness and vivid, yet realistic colors (in bright light conditions). E-PL1 is poor for shooting fast action, however, and T3i better. T3i was also better at video.
Then along came the E-M5. E-M5 can shoot 9 frames per second - faster than T3i and it focuses instantly. So E-M5 is good for fast action. Video is as good as T3i. Jpegs are better than T3i, though ironically, not quite as good as the E-PL1.
Bottom line is I'm pretty sold on compact system cameras like the micro four thirds offerings from Olympus and Panasonic. Only reason I came here today was to read owner experiences about the video performance of the T4i. The E-M5 video is pretty good, but I'm always open to something better if it should come along. The next big thing in video quality is likely going to be from the upcoming Panasonic GH3 micro four thirds camera.
It's hard to consider going back to the big Canikon cameras like the 7D, etc., once you've tried the compact system cameras and witnessed how you really don't give up much of anything important and in some respects they are better; e.g. the superb jpegs of the $280 Oly E-PL1. But again, if, and that's a big IF, a bulky, heavy Canikon came along with truly superior jpeg and video quality, I might consider it.