Commodity histories are in vogue these days (although nobody's yet written the one I really want to read, about cranberries); tea has been the subject of at least a few recently and also forms the basis for Laura Martin's Tea: The Drink That Changed the World (Tuttle Publishing, 2007).
This was an enjoyable, quick overview of tea's place in world culture, from the advent of its use in early China, Japan and Korea through its rise in popularity as a trading commodity as it came into fashion in Europe and America. Martin also includes information on the processing, brewing and marketing of various sorts of tea and how the beverage has evolved over the centuries into the version we know today.
The lack of citations, an index and a full bibliography bothered me, but as a casual examination of tea this was a worthwhile read. I learned a great deal about tea processing and varities, and the discussion of the current tea-growing industry around the world was enlightening. This is a nice book for a rainy weekend afternoon ... with a nice cup of hot tea at your side.