Kevin Mullins spent one day with the XF 23mm. He finds that “this is a FANTASTIC lens […] The lowlight performance of this lens is smashing. Absolutely smashing. The bokeh, especially in low light is just beautiful and the feel of the lens is great.” Read more and see the samples here at kevinmullinsphotography.
Another question: is it sharp wide open? David Hobby says here at google+: “Oh yes, yes is it is. Screamingly tack sharp.”