Never done it myself, but I know people who have. What I've found is that like most MA, it's all in how you practice it.
If all you ever do is go through the slow motion excercises without ever doing two man drills, sparring, push hands practice, hitting targets (heavy bags, etc.), then all it will really be for you is a good form of excercise. When practiced as a martial art, though, it can be effective.
So I've been told, anyway!
Regards,
Matt Wallis