I started using the XT1 for weddings in May. 7 weddings so far and two more this weekend. Speeches: Used to use Canon 70-200 2.8 L. Now using the 56 1.2 fuji. Except for one wedding all have been shot using natural light. No problems focusing but I now prefer to use focus lock on manual focus with the thumb button, which also focus's fine. Used flash once, off camera on manual with a lighting stand and focusing was no problem. ISO 1600. Also I have already mastered a quick turn of the ring to focus totally manually during speeches...very refreshing.
I find for dancing the focus is as good as or even, at times, better than my Canon 24-70mm. I use the 18-55 for dancing either no flash, mounted flash on stands or Nissan i40 or a combination. ISO 1600-6400. In low light in dancing I have very few problems, the 5d used to struggle at times in very low light. Using the tilt screen holding the camera high over heads in dancing is giving me a higher success rate than the Canon gave. I find that below 1/15 second dancing shots dragging the shutter gets a bit too blurred even with flash. Still really experimenting with dancing but getting just as good results and seeing more because of the EVF gain.