I haven't used it - I think there are better alternatives out there that support immune system health and cellular strength, a good prevention against disease. They did have a problem years ago with an ingredient that was proven to be harmful, but the company has had other endorsements of their business practices from objective sources.
However, I think it's dangerous for some people to throw around the words "pyramid schemes" - pyramids are completely illegal, and it's practically impossible to have a true pyramid when you have a real product involved. People pay money, buy a product, and receive it. That is NOT a pyramid. Any company that trades on the stock exchange (Dow Jones, NASDAQ, any of them) is absolutely NOT a pyramid - only one of the 50 State Attorneys General can prevent that from happening. There ARE people who do not understand network marketing and think it's somehow terrible or dishonest, even though corporate America has much more of a "pyramid" structure with people at the bottom getting no money and executives getting it all (think WalMart). So just because a company uses direct sales doesn't mean it's unethical - quite the contrary.
I think you need to figure out if there are stimulants of any kind in their products, and research alternatives that do not contain them. Does Herbalife use clinical studies, for example, and nutrition/food science in manufacturing their products? Do they manufacture them themselves or do they outsource to other places (or even other countries)? What precautions are in place to guarantee purity and quality of ingredients? Those are legitimate questions for any supplement company.