Objective-C Documentation

Here's a link to the documentation and also a link to a site that explains a lot of the basic grammar of the language. I always find it helpful to have documentation on hand, especially since it isn't really in  the book.

Documentation:
developer.apple.com/library/mac/#documentation

Tutorial Site:
www.otierney.net

Why do Objective-C files use the .m extension?

Here's a quick answer to this age-old question: "Why do Objective-C source code files use the .m extension?"  I was searching around teh interwebz and found this on StackOverflow.
Brad Cox, one of the two main creators of the Objective-C programming language, even chimes in and gives a funny alternative explanation of why this is so.