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: 
First of all, it's a very very personal question, and my first recommendation will be , if you think so, try Go for one month or so, learning the basics, and then deciding... Each one has the mind fitted more to some particular languages than another...

I also would recommend keep using both Python and Ruby, if you're interested, you have enough experience to use them comfortably (I think), so the next months you could experience a great boost in your experience using them...

For an strict utilitarian point of view, learning Go extensively could be a risk move, but worthy if begins to being using and you're one of the very few people with some experience when everyone are just beginning to learn the syntax...
Python is a available for most operating systems, it's generally accepted as a scriptin language, and it has matured to production quality.

Go is a research language that's only available in beta quality on Linux and OS X. Nowhere else. It's interesting from an intellectual point of view in that you can learn and apply a few concepts (typed channels combined with easy multitasking) that are otherwise difficult to use. 

As for Go, you might perhaps take a look at AT&T's "Plan 9" operating system first. It comes with a programming language called "Aleph" with also is C-based, has channels and multitasking. Looks to me like Go is a reimplementation of Aleph on more main-stream operating systems.