The X100 only has lag if one chooses to allow lag to creep in. For many, if not most, users of the camera, lag will be a non-issue due to the way they use the tool...
If one takes the stock camera out of the bag and simply stabs at the shutter release, then lag is going to be your companion...
I focus using manual focus actuated by the AFL button; recompose and/or first half-press shutter to lock exposure and then recompose; and wait for the moment.
Half pressing and waiting for the moment is the ideal method to eliminate lag with the X100. It's how I use my X100. Occasionally, though, things align without warning, or for some reason I am not ready, and a quick stab of the shutter release is the only way to get the shot. It's an exception, but it does happen.
In very low light, if I have not prefocused, there will be some AF delay. Keep in mind that the X100 does not have a focus-priority mode, so it will fire even if it has not gotten focus lock. To be sure that focus is locked, you need to wait for audible or visible confirmation. That adds some human lag. Fortunately, as light levels increase, the X100 will usually achieve focus with a quick stab, even if you do not wait for confirmation.
In a broad range of scene brightness levels, not too dark, not too bright, the X100 will AF and take the shot with very little lag, even without half pressing. It is a fact, however, that in bright light, aperture blade movement adds lag. Half pressing in anticipation is the only way to eliminate it. And in very low light, the AF slows down (although it is still very reliable.)
One situation that needs care is a series of casual portraits as the person changes expression or position. It is critical to half press immediately after each shot to be ready for the next "moment."
Jeff