The DrunkenBlog has a great inteview with Jonathan Rentzsch, a big time Mac Hacker. Buried in there is a plug for Python and PyObjC:

Objective-C's big weaknesses today is its lack of a Windows story, its lack of automatic memory management and its method call syntax, in that order.

That said, my eye isn't on Java or C# to put the knife in Objective-C's back -- it's Python. Python addresses all the issues and PyObjC makes it easy to use Python with Cocoa. Indeed, PyObjC can do things Objective-C can't do by itself.

but later on he also says this:

Windows is so backwards that the ancient Objective-C/AppKit was better. C#, while not aimed at Objective-C per se, gets them closer. So let's widen the gap again. It's highly arguable if Python is "better" than C#, but from a control-your-own-destiny angle, Python is a complete slam dunk. Python works well on *nix, Java, .NET and Mac OS X. It's open source. It's sane.

But I won't argue it's fast. It's usually just not so slow you care. (grin)

Speed *does* matter.