I've had my Mac for a little over a year, and I think it's overdue for me to learn Cocoa. I've looked around and Aaron Hillegass' book Cocoa Programming for Mac OS X seems to be the recommended book, so I will be getting that. But I was wondering if I should also get an Objective-C book? I have a lot of experience with object-oriented programming as well as C programming (and I'm getting into C++ now). Is there really anything special about Objective-C (versus other OO languages such as Ruby, which I use on a regular basis) that would require another book to learn about? Thank you in advance.