Hey everyone, I'm playing around with the Gosu game library now. (no pun intended)
It's not bad at all. The tutorial makes some things pretty self explanatory. (though it could use some more details, but what tutorial couldn't?)
Anyway, I highly recommend it, but if you're a complete beginner with Ruby (especially completely new to programming) it might be a bit much at once. But maybe not. It's pretty straight forward stuff.
I'm looking forward to soon trying out 'rubygame' as well and comparing the two.
I'm betting that Ruby may well take on Python in this department if more people give Ruby game development a try!