Autofocus Real-world experience:
Focus is usually acceptably fast, though anyone coming from an E-3 or E-5 is likely to find themselves disappointed, in comparison.
The way see it is this: if you're a Four Thirds lens owner and you're expecting full DSLR performance, you're going to be disappointed. However, if you want a camera that offers a considerable step up in image quality, that allows you to continue to take great images with your existing lenses and welcomes you into an impressive and growing new system, then you'll be delighted.
Which isn't to say the focus is bad - our first impressions are that the performance is consistent with Canon's EOS 70D, which offers some of the best live view focus of a conventional DSLR. However, for the very best performance, the E-M1 should be used with Micro Four Thirds lenses.
Continuous AF/Tracking
Continuous and tracking AF has been a stumbling block for mirrorless cameras, so far, because contrast-detection AF can't give the camera information about where to focus the next shot. The addition of on-sensor phase detection to the E-M1 promises to improve this - a concept several manufacturers are trying to develop.
Our initial impression is that the E-M1 is a step forward for Olympus (and Mirrorless cameras in general) - doing a pretty good job of tracking a target and getting a healthy proportion of shots in focus. Interestingly our tests so far have suggested that the camera will either tend to be significantly out-of-focus or absolutely tack sharp - a rather different behavior than we're used to seeing in DSLRs, where shots can prove to be a fraction out-of-focus once viewed on anything other than the camera's screen. We'll be conducting more tests and posting further conclusions soon.