Qt Creator 2.1.0 brings enhanced Qt Quick and mobile applications support
labs.qt.nokia.com
labs.qt.nokia.com
For example, it does excellent semantic syntax highlighting where the same variable is drawn in the same color throughout - after using it for a while, code in other editors looks pretty dead :-).
And FWIW, considering that KDE apps do work on and get shipped for Windows and Mac OS X, that "only platform" is a pretty broad one. Actually I can't speak to how complete the port of KDevelop's own application logic to those platforms is as I haven't tried it there, but I certainly happily use apps like Okular and Gwenview on Windows 7. Here are shots of that too, while we're at it: http://simplest-image-hosting.net/png-0-windows and http://simplest-image-hosting.net/png-0-capture24
That shows some of the issues I have with it - I don't like the custom theming, especially given how inconsistently it's applied (still uses system looks for scrollbars, the menu bar doesn't fit at all, etc.).
I really wish the various teams working on open source IDEs would work together to make one very good IDE with a good plugin infrastructure to support the union of their features, instead of a zillion quite-good-but-not-it ones.