Qt Creator looks bad on OSX with a retina display because by default pixels are simply scaled up so that one ordinary pixel equals 4 retina pixels. Text becomes hard to read and looks jagged.
Text can be displayed at the native 'retina' resolution by adding just one key to the info.plists file within the app bundle, as discussed here:
It would be great if this fix were included in the next QT Creator version so that those with retina displays do not need to do this manually.
For full Retina support, the application icons on the left bar would also be updated, but this is far less important.