It's my opinion that if you use it judiciously, it is not harmful... unless you've got some sort of pre-existing medical condition that it might aggravate. (ie- heart murmurs, high blood pressure, etc.) I feel that ECA, as well as NYC (norephedrine, yohimbine, caffeine), are the best legal choices for burning fat and also holding onto as much lean muscle as possible while restricting calories.
Consumer Reports and other advocacy groups want it banned, saying how harmful it is... but most of the deaths or serious problems they cite came from people abusing ECA or other ephedra products.
Some real side effects you should keep in mind:
It can result in swelling of the prostate gland, and make urination difficult. I never noticed this when I took it when I was younger, but now that I'm getting older, it's become noticable.
In a lot of people, it will also kill the ability to get an erection while it's in your system. (Your sex-life is absolutely none of my business, but keep this in mind if 'performance' is important to you.)