Question: I was reading about Go, and I can see that it's very good and can be a language used by many developers in some months, but I want to decide a simple thing: **Learn Go or improve my Python or Ruby knowledge?**

Years developing with Python: 1  

Years developing with Ruby: 0.3

Answer: 
In reality, you should do both; if it's what you want. For me though, out of the two, I'd only look at Python. I have no real interest in languages that are so new.
It's not easy to answer this without knowing how good your Python is, or what you do, or where you'd use Go. If you're looking for employment, I suspect Python is the way to go. I'd be surprised to find anyone is using Go for major projects at the moment (outside Google).

Note also that Go is by no means finalised. See [here](http://go.googlecode.com/hg/doc/devel/roadmap.html) for the Go roadmap, and note the potential changes in the future. So you may be trying to hit a moving target currently.