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: 
It's up to you. You should probably do both if you can, because that way you will have more tools on your metaphorical programmer's belt.

There are a number of things that I think are worth considering whenever I'm in a similar dilemma.

Is a new language (not just unfamiliar, but actually new, like Go) likely to catch on? (If so, it will become practically NECESSARY to learn it, rather than just a good idea.)

You will need to spend some time to learn the unfamiliar language. Will this time investment result in some sort of positive return? The obvious one here is development time (i.e., can you eventually get more done and get back the time you spent to learn it), but if the language is superior in other ways (runs faster or with less memory, is best for your particular problem domain) those might factor in too.

Will learning the unfamiliar language allow you to solve a relevant/important/urgent problem that cannot be solved with what you already know?

Unfortunately, none of us can tell you how to weigh each of these concerns. You'll need to think about it really carefully and come to the answer on your own.
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.