How exactly is the I CHing used in daily Chinese life; how many people use it,
and how do they interpret it to use in ordinary daily life?

I didn't find an answer to all your questions, but did find this one
short statement on a website that I wouldn't necessarily trust as
authoritative --

"The tradition is still maintained today in many communities, although
officially the oracle has fallen into disuse on the mainland of China.
It is widely studied in the modern universities of Japan, and is
employed in business negotiations in many parts of South-east Asia."

http://www.indobase.com/iching/history.htm

--K~