When I worked at the Apple Store, I was complaining to a customer that they didn't sell any books when it came to coding (everything had to do with using your ipod and beginners guides to the OS). Turns out this customer was from SV and worked for Apple, although he never mentioned what he really did. He suggested that if I "want to make money" to learn AppleScript. I taught myself by just reading tutorials online, and learned you can do some pretty cool stuff with AppleScript. However, I personally would say one should put more focus on Objective-C and Cocoa. I began doing that (many tutorials online), but soon after got into web apps and put my focus elsewhere.

So, in my opinion, get a feel for AppleScript, then move on to Objective-C and Cocoa.