I've always wanted to get into Cocoa programming. I like the look and feel of a good Cocoa app, and folks I respect tell me that it's a wonderful environment. But, to be honest, I've always been somewhat put off by the way that Cocoa programming is tightly coupled to Xcode and Interface Builder. I've never really liked IDEs, simply because in the past they've felt like they're in my way.
So then Daniel Steinberg twisted my arm and got me to edit his new book, which introduces Cocoa programming to people who are already programmers in some other OO language. Trying to be a good editor, I gritted my teeth are fired up Xcode and started to follow along with his tutorial chapters. And, somewhat to my surprise, I had a working (if minimal) web browser up and running in a few minutes. I added buttons, and later a progress bar, and it all just worked. So now I've changed my opinion. Cocoa is a really well thought out framework, but the tight integration with Xcode and IB make it very, very sweet. I'm looking for an excuse to spend some serious time writing a decent-sized app with it.
In the meantime, if you're like me, and want to dip a toe into Cocoa development, I'd recommend his Cocoa Programming: A Quick-Start Guide for Developers. If you're more of a hands-on learner, the good news is that Daniel and Bill Dudney will also be running a great 3-day Cocoa Studio at the end of October. It's in the amazing Inverness facility in Denver (which I'm at right now, teaching a Rails Studio with Chad).