ephedra is just the plant that the alkaloid ephedrine is from. I've taken it many times for all-niter studying when better stimulants weren't available. The energy of an amphetamine without the pleasure. But I didn't take it regularly, like some people do for weight loss; there are better drugs for weight loss, don't waste your money on ephedrine.
If you are young and healthy and use it sparingly, you'll be fine. But, using it reguarly in the doses that most people do does increase your risk for a variety of cardiovascular conditions, even if you were otherwise healthy.
The reason it's banned in some states is partially because of the media hoopla over its safety, but mostly because it's an indirect precursor to methamphetamine, like another poster pointed out. Fun Fact: Amphetamine was invented over concerns that the Chinese would cut off the supply of ephedra; what ended up getting invented (l-amphetamine) was thought to be a huge medical breakthrough at the time and prescribed for everything and in big doses.