Try to be friendlier to small screen sizes. Use 800x600 if width/height of 2/3rds is smaller than 800x600 (things don't look smaller than that size), use desktop size if it is for some reason smaller than 800x600

#include <QtGui/QApplication>
#include "mainwindow.h"

int main(int argc, char *argv[])
{
    QApplication a(argc, argv);
    MainWindow w;
    w.show();
    return a.exec();
}