There is a new infomercial out there claiming the wonders of a prickly pear fruit. It looks very expensive. The concept is that the cactus has rejuvenating properties because it has to grow in such a hostile environment.
We studied something like this in my Biochemistry course. Anything living in extreme environments has something called heat shock proteins. The concept of the cactus as a health food is that by eating it, you will be able to make your own heat shock proteins and that it is a cure for whatever ails you. I don't believe it, but on the other hand they are also saying that eating cold water fish is good for you and they would also have heat shock proteins. The ad I saw was based on the Nopal or Prickly Pear cactus. One thing it is not is cheap at about a dollar per ounce:
Nopal Party Cactus
The other big wonder cure nowadays is kombucha tea which is about a tenth of the price of the prickly pear drinks. People who like that often make there own.
I just saw nopal in pill form and it had all of one gram of cactus in it per pill. I don't care how effective it might be, I don't think a gram of any plant is going to do much for you!