All kidding aside, Objective-C isn't the sort of language people use because they want to. Rather, they use it because it's what Apple says they can use.
Back in the NeXT days, we used it because it was far better than anything else out there. But that was 20 years ago. Times have changed, and we have better programming languages available to us. Even with Objective-C 2.0, it's still somewhat of a relic.
Well, over the past 20 years I've played around with a lot of languages and a lot of environments and I do enjoy writing in Objective-C. It makes a few neat things that I like easy, like Duck Typing and delegates. But more than the language I enjoy Apple's APIs. They are very consistent and nicely done. I know it wasn't always like this, and there are still a few dark corners if you really dig into non-common areas, but all in all it really is fun to use. More fun than most C++ APIs, IMHO, and to me also more fun than .NET or Java. I like C# as a language, but I can't stand the .NET API. Likewise, Java as a language is OK (neither great nor bad) but the API is so-so. It's good, but I never really enjoyed using it. But I can say that I do enjoy Cocoa.
One thing in particular that I like is that due to a few Objective-C language features you can often avoid creating yet another subclass of something, thanks to Duck Typing.
Now they even added support for C blocks allowing easy anonymous callback functions, which enables a few more neat programming patterns. My favorite scripting language is Ruby and Objective-C is the compiled language that comes closest to it allowing me to make use of design patterns that I learned to love via Ruby.