I recently upgraded to the 70D from the 550D (T2i), so my situation is a bit different but here are some thoughts:
Pros:
- I am happy with the ergonomics -- but this is personal;
- I do not mind having a slightly smaller camera than the 7D, since I hike quite a bit with it;
- the dual pixel Af works reasonably well -- liveview shooting is actually pleasant now! -- and lets you take full advantage of the swivel screen for shooting at extreme angles;
- IQ is a bit better than the T2i/7D: noticeably more resolution, a little less noise and the noise that is there seems easier to be treated with lightroom/PS. I now shoot more confidently at iso 800/iso1600 in raw
- Fast buffer! With a fast card I get 21 raws at 7fps before slowing down.
Cons:
- it does feel a little less rugged than the 50D or 7D (that I used in some occasions);
- I managed to get a little spot on the viewfinder/focusing screen after a few indoor uses -- not sure what went wrong, I have been reasonably careful but I cannot blame the camera design for sure;
- it does not work with kenko teleconverters w some lenses IF YOU HAVE AF MICROADJUSTEMENTS ON.
- the main dial is a bit too easy to turn, for my taste;
- battery life takes a huge hit if you use a lot of liveview focusing -- keep spares at hand;
- the AF phase detection sensor is the same as in 7D but it does not allow for

1) spot AF (different, smaller point than single point AF); and (2) single point expansion;
As I do a lot of bird photography, I would have really liked to have at least (1). Let's hope a firmware will come.