Benefits of Oolong
Oolong tea has been used in Traditional Chinese Medicine for hundreds of years, and has been shown in scientific studies to play a role in the oxidation of fat. As one would expect, tea generally has no side effects, but neither is it a miracle-worker. TCM takes a holistic approach to the health, so a practitioner would never prescribe oolong alone for the treatment of obesity, or any other problem.
There are many varieties of oolong, one of the most famous of which is harvested in the Wuyi Mountains of the Fujian Province, which, presumably, is where the Wu-Yi Source got its name. However, it is unclear whether or not the Source's tea is indeed from the Wuyi Mountains. Ironically, the Source's "source" is never credited.

Stategic fonts and photos of Chinese teapots imply the suppression of this "natural" cure by Western medicine. The Promotion of Wu-Yi and Wu-Long
On the Wu-Yi Source website, a list of benefits for the product is worded as follows:
1) May brighten skin while improving skin clarity
2) May fortify your immune system
3) May promote stronger, whiter teeth
4) May enhance body-mind wellness
5) It is 100% Natural and Organic
It is interesting to note that each of these claims, except the last, is preceded by the word "may." In addition, though each site has half-a-dozen written testimonials, there are none of the obligatory "before/after" pictures, and the fine print carries the typical disclaimers "Results Not Typical" and "When Used in Conjunction with Diet and Exercise." On the Wu-Yi Source, there are pictures of reputable health magazines strategically placed alongside a few testimonials of particular interest, but nowhere does it explicitly state that these magazines have endorsed Wu-Yi, though that is the implication.