If you make a new project and try to debug/run you might get the following error.
Unable to start 'org.qtproject.example._8paint'. Debugging has failed
Starting remote process. Unable to start 'org.qtproject.example._8paint'
Notice the extra underscore in front of the program name. Apparently, your program's name is not allowed to begin with a number or an underscore.
edit: This error should be resolved in Qt 5.3