I am a big fan of tea. My screen name here is from my favorite kind of oolong, Ti Kuan Yin (Iron Goddess of Mercy). Caffeine isn't particularly good for you, I think is Dr. McDougal's stance. I'm also somewhat sensitive to caffeine so I stay away from it. Caffeine and sugar together come close to making me pass out.
BUT.
Not all teas are as caffeinated as coffee, and I am not sure if there's a reason for this or if it's just my own biased perceptions, but the more typically Asian, less fermented teas do not affect me as strongly as black "breakfast" tea or coffee. So maybe they are less potentially harmful.
In any case, green tea is significantly lower in caffeine than coffee (
http://coffeetea.about.com/library/blcaffeine.htm ) and has antioxidants and, I've heard, great anti-aging properties. Cold, unsweetened green tea seems like it would be a great beverage for MWL because it has no sugar, and tastes great.
I do not know what Dr. McD would say, but green tea is definitely a big part of the Asian diet, and it's good qualities may balance or outweigh the bad. I think it is a much healthier way to treat oneself than coffee is, at least. In the winter especially, sometimes you just need a good hot drink.
(I get my tea from a couple local shops and order from
http://www.adagio.com/ if I can't find what I'm after. I really enjoy gyokuro and genmaicha green teas.)