I am a rare (for Hacker News) C# dev and I've just been toying around with Go. There is stuff to like but my feeling is that the biggest weakness of the language is that it is designed to solve the problems that Google has (surprise), which is only a fraction of the problems that the world has.

It is a scalpel verses a swiss-army knife. The question is which do you need.

If you are doing Internet-related things (server-side plumbing and apps, not search), it looks like a pretty darn good fit. It naturally leads you build up a set of small start tools that you combine to build a larger service. The channels metaphor is a really nice way to deal with concurrency.

If you are building anything else (desktop, LOB apps, DB front-ends, mathy stuff, etc.), it looks a bit limited. For example, it doesn't have a modulus operator. Not a big deal but it shows that the language designers are more concerned about supporting their target domain than supplanting Java, much less C#.

Really, the thing that I fine the most troublesome is this feeling that the designers of the language have such a focused vision that it will hinder the growth in the future but, for now, it needs that to keep from becoming overgrown like C# is.