Conclusion
PythonWorks and Pythonwin are very stable—I worked on a few reasonably large projects, and they haven't crashed. IDLE is quite stable, too, with the exception being the version delivered with the Python 2.0 beta. But then again, that's beta. The version of Wing reviewed was the first beta and wasn't quite stable enough for real work. But the second beta of Wing looks much more stable, and I successfully used it for my largest project, Kura.
PythonWorks looks the most professional. But it is difficult to decide who it was written for. The whole interface looks like it's been made especially for newcomers to programming, but it's only customizable by experienced Pythoneers. It is stable, has some nice features, and a good debugger, but I don't think I can recommend it for large projects, mainly due to the lack of a source browser. As it is, I don't think it's worth the $935 price tag, especially for professional developers or open source hackers. I can imagine a school wanting a good, stable IDE to use in teaching their pupils a decent object-oriented language buying a classroom full of licenses, if they can get a discount. It might be ideal for teaching purposes.
Wing IDE, the second commercial IDE, shows a lot of promise. The interface needs a lot of tidying up—I feel it takes up too much screen space, and some actions are not comfortable enough. But it has the best source browser I've ever seen, the project management facilities are good, and the editor is Scintilla, which is excellent. Despite the fact that this is a commercial IDE, source is provided when you buy a license, and Archeopteryx have released their Python bindings to GTK Scintilla under GPL. Open source hackers get a free license, too, as long as they are not selling their work. Archaeopteryx is working very hard on delivering a stable release. Wing IDE is a good product, a real powertool, and I think that the next version will be well worth the money—when the bugs have been ironed out.
Pythonwin is simply the best IDE for Windows users. Although it doesn't offer as many powerful features as Wing IDE, it's stable and has a clean and productive interface. The source browser is decent, the editor is very good—Scintilla, of course (but with folding enabled!)—and the debugger good enough. It's a pity it's Windows only—it's the only Windows application I've ever seen that almost seduced me to work using Windows!
IDLE has little to recommend itself. In the last version I used for real work, the class browser still had a lot of GUI problems. The interface is not well thought-out; with its enormous edit menu, the debugger is not really usable, and the application feels very, very slow, even on large machines.
But on the whole, the dearth of Python IDEs is a thing of the past. Every developer should be able to find something suitable for his or her needs, and the future looks set to become even richer with, for instance, the release of Eric, and the final version of Wing IDE.