I have been using the OM D E-M5 for a few of weeks now. It definitely has the best image quality of any of the u4/3 cameras I have tried. So I should be delighted it is a big improvement over the first u4/3 I used, the Panasonic GF1, which was already "good enough" image quality when factoring in weight+size / image ratio for me to decide I would ditch my full size DSLR. I do recommend the OM D. That said, I was a bit disappointed… because I was hoping for something unrealistically great. So my caution is don't get too caught up in the over-hype. the OM D is incremental improvement, not revolutionary improvement. There are a number of reviews online which claim it's image quality is in the same league as the better APC size sensors like the Fuji X-Pro1 or full size sensors. Under perfect lighting conditions this might be true, but in the real world, with challenge lighting situations it's shortcomings can become apparent compared to a number of cameras with larger sensors (especially at ISO 1200 or above). Thankfully, a lot of backpacking imagery can be shot at lower ISO, so unless you are doing action shots of animals with long lens or not using a tripod in for the daybreak / sunset shots, this shouldn't be too much of an issue.
One point of reference… a couple of weeks ago I shot an evening concert using the OM D and a Fuji X-Pro1, often with fairly similar quality lens mounted. I had to shoot in avail light, no flash. After the concert I showed the pictures to a number of folks. Even the non photographers consistently preferred the X-Pro1 image quality… this wasn't pixel peeking, but looking at full screen images on an iPad3 and Apple cinema display. There were a couple of shots from the OM D that were remarkable, even at ISO 3200, but most were merely OK after a bit of work in Photoshop.
Just a few years ago I remember a number of my photo buddies longing for a moderately size camera that had good image quality and many of them wondering if anyone would make such a camera. We now have numerous options to choice between. My personal recommendation would be that the OM D is the best compromise (lens choice, image quality, features). If you have to shoot in low light or are looking for maximum detail in a compact camera, and you can live with the limited lens choices, then Fuji X-Pro1 is has the most excellent, just keep it mind that it is kind of unfinished with a quirky UI and mediocre autofocus.
I am using both of these cameras depending on my needs… but I have to admit, my everyday carry camera, and the camera I find myself reaching for the most is the Fuji X100. It's quirky, feels not completely finished, but it hits my sweet spot. I really enjoy using it most of the time. I find the fix lens liberating rather than restrictive… maybe's it's because I spent so many years shooting with either a 35 or 40mm rangefinder.