I'm in the planning stages of developing a cross platform (Mac & Windows) app. Performance is not an issue, and Python would be a good fit for the problem domain. I'm a Cocoa developer with pyojc experience. Cocotron looks appealing, but has anyone used Cocotron with pyojbc?
If not suppose the alternatives are either Cocotron with Objective-C or Python with wxwidgets.
If the performance is not an issue, then why not to use just python without obj-c? wxPython will provide native look and feel on both Windows, Mac OS and Linux. And it's easy to make distributions for different OSes with py2exe and py2app (and linux users have python anyway :-).
BTW: there is a great example of wxPython open-source application - Editra text editor. Also, the author of this program wrote a nice book on development of cross-platform apps with wxPython. I'm currently reading it and I enjoy it's short and laconic style. If you want to buy this book - you can complete a survey on the publisher's site and get 50% discount :-) that's what I did.