If you are to believe the article, and my limited experience, the popularity of Go stems from its simplicity, approachability, and performance. It's easy to jump into Go and get some really nice results. As far as what it's meant for, I don't know for sure. A "garbage-collected systems language" is an oxymoron to some people, but not to others.
Seems like Go is probably going to fill the niche between higher-level compiled languages (e.g. C++) and popular dynamic interpreted languages (like Ruby or Python). Got a big compiled C++ application but wish your language was less crufty? Go might be for you. How about a Python programmer who's itching for type safety and performance? Go is again probably a good fit.