Here is an interesting dpreview post about how Fuji's manual focus ring works:
The resolution of the X100 MF ring is not a problem. It generates one pulse every 3 degrees (120 pulses in one full revolution). Theoretically only one half turn of the MF ring is required to bring the focus from infinity to about 1.8m (try this by slowly turning the ring). This should be good enough.
The problem is in the way X100 processes the MF input. When the ring is turned fast, most of the pulses from the ring are missed by the processor. In fact it is worse: the faster you turn the ring, the more pulses are missed and the more turning is required to cover a particular focus range. An impatient photographer will find himself spinning the ring forever.
Another observation: in low light the manual focusing is worse than in good light. This confirms the theory that the processor is busy metering or whatever and can not detect all the pulses resulting from the MF ring rotation.