Green tea has been mentioned many times on Oprah's TV. show, and also in her magazine
Oprah knows a good thing when she sees it, and judging by the amount of times she has mentioned green tea I would say that it gets the Oprah Winfrey seal of approval.
A quick search through Oprahs official site has links to the health benefits of green tea, tea samplers, green tea weight loss information, and even green tea cocktail recipes(LOL, i'm not sure how healthy that one is).
I really like this one "The Okinawa Program" which lays a plan for defying age.
Oprah has access to the best nutritionist money can but, and she has built up some major credibility by only recommending quality stuff - so this is just on more reason to to keep sipping on green tea.