I've been using Go on the side since mid-late 2013, so not nearly as long as some here, but I was heavily impressed by both Goroutines and channels as ideas, and by the net/http library.

The general portability and simplicity of the language has made it nice for side-project work.

I've since used go to write a blog engine, several APIs for school projects, and have been working on a scripting language (pisc.junglecoder.com).