If you get some good clients you can make a lot of money, but you've always got to be looking for future work. If the work drys up, what are you going to do? Also some people don't like your work, so you have to re-do it. This is all coming from web designer friends, personally I wouldn't get into it.
Just re-read your post, working for a company would be a safer bet. Probs worth doing!