The animation is fluent on my machine but you can try this:

Qt Code: 
  1. #include <QtGui>
  2.  
  3. class MainWindow : public QMainWindow
  4. {
  5.     Q_OBJECT
  6.  
  7. public:
  8.     explicit MainWindow(QWidget *parent = 0) : QMainWindow(parent){
  9.         QVBoxLayout* layout = new QVBoxLayout();
  10.  
  11.         pushButton = new QPushButton("start");
  12.         textEdit = new QTextEdit();
  13.         layout->addWidget(textEdit);
  14.         layout->addWidget(pushButton);
  15.         QWidget* central = new QWidget();
  16.         central->setLayout(layout);
  17.         setCentralWidget(central);
  18.         connect(pushButton, SIGNAL(clicked()),SLOT(start()));
  19.     }
  20.  
  24.     QPushButton* pushButton;
  25.     QTextEdit* textEdit;
  26.  
  27. public slots:
  28.  
  29.     void start(){
  30.         scene = new QGraphicsScene();
  31.         text = new QGraphicsTextItem();
  32.         text->setDocument(textEdit->document());
  33.         text->scale(6,6);
  34.         text->setPos(-100,0);
  35.         text->setTextWidth(140);
  36.  
  37.         scene->addItem(text);
  38.         scene->setSceneRect(0,0,400,400);
  39.         view = new QGraphicsView(scene);
  40.         view->fitInView(view->sceneRect(),Qt::KeepAspectRatio);
  41.         view->setRenderHint(QPainter::SmoothPixmapTransform);
  42.         view->showFullScreen();
  43.  
  44.         // the important part:
  45.         QPropertyAnimation *anim = new QPropertyAnimation(text, "pos", text);
  46. 	anim->setStartValue(text->pos());
  47. 	anim->setEndValue(QPointF(-100, -1000));
  48. 	anim->setDuration(5000);
  49. 	anim->start();
  50.     }
  51. };
  52.  
  53. #include "main.moc"
  54.  
  55. int main(int argc, char *argv[])
  56. {
  57.     QApplication a(argc, argv);
  58.     MainWindow w;
  59.     w.show();
  60.  
  61.     return a.exec();
  62. }
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