Hmmm, I think that drinking tea prior to a workout is a good idea. Just as long as you are making sure to stay hydrated. This may be all mental, but atleast for me, drinking tea helps to revitalize my mind. It helps to wake me up from my "sleepiness" and live in the present. This is why I will sometimes drink a cup of tea and meditate before I go in for a long training session, exam, or tournament. It helps me to feel more at peace I guess. Though I don't drink just any old cheap tea from the grocery market, I actually bring back my own tea from China whenever I visit my family there. I usually drink Pu-ehr tea. It is very good, but quite expensive relative to other teas.
So basically, I personally would recommend to drink a cup of good quality tea before a long day, just make sure to stay hydrated...maybe drink some gatorade beforehand as well. ^_^
Proud student of Grandmaster Yong Sung Lee, founder of Hapmudo