I thought I'd share a couple of things about the OMD E-M1 and the Eye-Fi combination. Today I photographed 170+ abseilers on a job at Old Trafford, the home of MUFC..
I used the Eye card to transmit to a laptop. It worked flawlessly,.....ish!! :) When transmitting it never skipped a beat and saved us no end of hassle. However, on a couple of occasions it just simply refused to transmit. I restarted the router, I restarted the laptop and I just could not get it to budge. A few minutes later I spotted that the battery light was flashing on the camera indicating that the battery needed replacing. Suddenly the Eye-Fi card once again swung into action. Writing this now it becomes apparent what was happening but in the heat of battle it doesn't immediately hit you. Unfortunately I needed to change batteries quite a number of times (personally my only real complaint with this camera), and it was on the 3rd or 4th time of the Eye-Fi card stopping that it dawned on me.....If the camera battery is getting low, it will not power the Eye-Fi card, and thus it will not transmit. And more frustratingly (unless I'm doing something wrong), one would expect that the battery grip would negate this problem. But it doesn't. If your battery grip battery is getting low the camera does not draw from the still charged camera battery, so the Eye-Fi just ....stops!!
On the plus side, it's nice to see a little icon when reviewing images on camera to let you know that your image has been successfully transmitted by the Eye-Fi card.
I hope that all makes sense! :)