I make about $100 dollars a month on the side with it. I don't really try for Amazon, most of my sites are Adsense related.
Is it worth it? I don't think I would use Amazon only. There are too many other affiliates that pay a lot more money and the cookies stay much longer.
But, I have been surprised before at what people buy that isn't related to what I promoted. So I think it is like anything else - if you like the idea of making money on Amazon and stick to it, you can do it.
But beware, Amazon has discontinued affiliates in some states due to tax laws. You can get around this by registering a business in another state, but there is that to think about.