Go's Disadvantage

I've been learning Go for a while and found that it has a lot of good features (simple and clean syntax, fast compilation/execution, good support for concurrency, first class functions, etc). But very few popular projects are developed in Go.

I'm just wondering what are the main disadvantages that restricts Go from becoming a mainstream language? Can someone come up with a kind of program/project for which Go is obviously not suitable to be used?

Go is only 3 years old. C is more than 40 years old. C++ more than 30. Perl 25. Ruby almost 20. Java is a relatively young language at 17, and C# quite young at 10 (or 12, depending on how you count it). And Java and C# had a lot of resources thrown at making them dominant, with Sun and Microsoft investing in all kinds of tools and libraries and getting people trained in them. Compared to that, 3 years is almost nothing. Google spends some money on developers for Go, but at nowhere near the scale of C# and Java. And 3 years isn't a lot of time for really prominent products to be written and released in Go.

Give it a few years. Write some code in Go. Maybe yours will become the next prominent project.

As far as what it's not suited for, it's not suited for anything that requires a really mature language and toolset. If you want fancy refactoring IDEs, tons of off the shelf libraries, and lots of tutorials and information online, you probably won't find that yet. The last I checked, its garbage collector was a little weak; it's possible to get leaks due to mistaking integers for pointers, since it's a conservative collector. This could be fixed by now, but its indicative of the relative immaturity of the Go implementation; there are certain things that may be solved problems in other languages (or have well-known workaround patterns), which are still a bit up in the air for Go.