With a pruned wallet possible in master I believe we should expose the option in the GUI.

The Main tab in preferences will offer a chance to toggle the node type and size.
<img width="612" alt="pruning_gui_off" src="https://cloud.githubusercontent.com/assets/216917/8766147/834fb842-2e2c-11e5-94b0-c342132243bf.png">
<img width="612" alt="pruning_gui_on" src="https://cloud.githubusercontent.com/assets/216917/8766148/8351a0c6-2e2c-11e5-841b-af02fd77ff44.png">

The prune size UI should not permit sizes less than 550.

{
    this->model = _model;
    if(_model)
    {
        
        if (_model->isRestartRequired())
            showRestartWarning(true);
        QString strLabel = _model->getOverriddenByCommandLine();
        if (strLabel.isEmpty())
            strLabel = tr("none");
        ui->overriddenByCommandLineLabel->setText(strLabel);
        mapper->setModel(_model);
        setMapper();
        mapper->toFirst();
        updateDefaultProxyNets();
    }
    
    
    connect(ui->databaseCache, SIGNAL(valueChanged(int)), this, SLOT(showRestartWarning()));
    connect(ui->threadsScriptVerif, SIGNAL(valueChanged(int)), this, SLOT(showRestartWarning()));
    
    connect(ui->spendZeroConfChange, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
    
    connect(ui->allowIncoming, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
    connect(ui->connectSocks, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
    connect(ui->connectSocksTor, SIGNAL(clicked(bool)), this, SLOT(showRestartWarning()));
    
    connect(ui->lang, SIGNAL(valueChanged()), this, SLOT(showRestartWarning()));
    connect(ui->thirdPartyTxUrls, SIGNAL(textChanged(const QString &)), this, SLOT(showRestartWarning()));
}