http://www.gardfoods.com/coffee/coffee.coffee.htm
A pretty comprehensive, if informal, history of humans' interaction
with the coffee plant. People have been chewing coffee berries in
Africa for 100,000 years or so. Coffee was definitely growing in
Yemen, where it is not native (so must have been planted), in 525 AD.
The list of links in this chapter, often becomes outdated,
therefore you might wish to use the excellent
Way-Back Machine to find them again:
http://www.archive.org/