How many people in the world habitually use chopsticks as opposed to
knife and fork, knife and fingers, fingers only or other combinations
of implements I haven't thought of? How are these figures arrived at?

This may be of interest:

"It is estimated that 1.5 billion people worldwide use chopsticks
every day, usually beginning between three and four years of age."

http://www.bu.edu/phpbin/researchbriefs/display.php?group=bridge&date=2003-12-12

Thank you for your very rapid response. 

The figure of 1.5 billion is roughly what I came up with when I added
together the populations of China, Taiwan, North and South Korea,
Japan, Vietnam, Laos and Cambodia. However, I was hoping for something
a little more authoritative.

I would also like, if possible, to be able to compare the popularity
of different sets of eating implements.