The point you have to remember is that it is trained on bulk data out there in a very inefficient manner, it needs to see thousands of examples in order to start getting any sort of understanding of something. If you ask it "how do I do {common task} in {popular language}" you will generally get excellent results, but the further you stray from that the more likely to be error prone it is.

Still it is often good to get you looking on the right track when you are unsure to start, and is fantastic for learning a new language. I've been using it extensively in learning C# where I know what I want to code but not exactly how to use existing features to do it.