Remember for all case reports under these circumstances its worst first. There are no population surveys to find mild or asymptomatic infections and there wont be for a while.
4% is probably too high.
I tend to agree with you
While WHO reports the fatality rate at 4%
initial reports from Chinese authorities originally stated fatality rate at 2%.
Although the Chinese authorities are not known for candor, or timeliness,
and tend to minimize their conditions until it seems out of control(ie.:SARS, pork virus)
Comments made tend to indicate that the incubation period until 'full-blown'
seems to be an incubation period of between 8 -14 days.
Also not known is whether other medical pre-conditions may have contributed
to the initial fatality rate, such as diabetes, blood infections, cancer treatments,
suppressed immune system, prior bouts of pneumonia, etc., etc.
Due to the unknown and novel characteristics of the virus, there is little known about
at what stage does it becomes communicable, and infect others.
Since this is an air-borne disease, minimizing contacts with others and avoiding groups
with either known, or unknown viral exposure, seems to be prudent.