Even though the auto-focusing is a bit slower than most DSLR's, it is more than adequate and once focus is achieved, it is right on!
Will it replace my full frame Nikon D800? No of course not. For the moment there is clearly room for both. The X-E1 will go on my travels whenever I need to go light. I do however believe that the D800 might be the last DSLR body I bought. The future of the mirror-less is surely exciting and I sincerely believe they will eventually replace most if not all DSLR bodies.