Personally, I'm not a big fan of O'Reilly programming books. They're all about syntax, with no useful examples. I haven't read the Ruby book, but I went through the Python book, and although I "understood" everything, I found it somewhat hard to start my first program. A syntax book would be useful if I was porting something from one language to another, but if I'm trying to learn and understand a new language, I like more examples.
But honestly, everyone's different. In my experience, as far as programming books go, the style/approach of the book is just as important as the material. If you can learn Python and Ruby just by looking at syntax, then maybe those books will work for you.
You might want to check your library and see what kind of books they have. Even if you can't find anything superb, it might help you realize what style of book would work best for you before you shell out 25-35 bucks for something that got good reviews on Amazon.