If you know Python or Perl, you'll have Ruby 20 minutes after visiting TRYRUBY.HOBIX.COM; then you just need to keyword-bookmark the Ruby core reference, so you can type "ruby String" in your URL bar and get the String class reference.
Not saying this book is bad or anything, just saying: Ruby really is that close to every other language you've used.
Except for the emphasis on lambdas and closures which might be a conceptual hurdle for somebody coming from a language where they aren't used very often.
You don't really need to think about closures to write idiomatic Ruby code, even though closures are being relied on heavily behind the scenes.
I think tryruby does a good job walking you through blocks, and if you have blocks you have lambdas. So I'm not saying "if you know Python you know Ruby"; just "if you know Python you're a 20 minute web demo away from knowing Ruby". ;)
Not saying this book is bad or anything, just saying: Ruby really is that close to every other language you've used.