PythonQt is distributed under the LGPL 2.1 license. It can be used in commercial applications when following the LGPL 2.1 obligations.
The build system of PythonQt makes use of a modified version of the LGPL'ed QtScript generator, located in the "generator" directory.
See http://qt.gitorious.org/qt-labs/qtscriptgenerator for details on the original project. Thanks a lot to the QtJambi guys and the QtScript Generator project for the C++ parser and Qt typesystem files!
The PythonQt wrappers generated by the generator located in the "generated_cpp" directory are free to be used without any licensing restrictions.
The generated wrappers are pre-generated and checked-in for 5.0, 5.3, 5.4 and 5.6, so you only need to build and run the generator when you want to build additional wrappers or you want to upgrade/downgrade to another Qt version. You may use the generator to generate C++ bindings for your own C++ classes (e.g., to make them inheritable in Python), but this is currently not documented and involves creating your own typesystem files.