What I like about Qt and PyQt is that it is so much more than just a GUI framework.

It's got a powerful set of XML parsing classes, a file system that automatically takes care of the difference in file path formats between Windows, Macintosh and Linux, cryptographic hash classes, and support for SQL databases.

There is also a "settings" class that allows your app to remember settings between executions. Behind the scenes it uses the registry in the Windows environment, XML files on Macintosh, and ini files on Linux.