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.

}
            break;
#endif
        case DisplayUnit:
            setDisplayUnit(value);
            break;
        case ThirdPartyTxUrls:
            if (strThirdPartyTxUrls != value.toString()) {
                strThirdPartyTxUrls = value.toString();
                settings.setValue("strThirdPartyTxUrls", strThirdPartyTxUrls);
                setRestartRequired(true);
            }
            break;
        case Language:
            if (settings.value("language") != value) {
                settings.setValue("language", value);
                setRestartRequired(true);
            }
            break;
        case CoinControlFeatures:
            fCoinControlFeatures = value.toBool();
            settings.setValue("fCoinControlFeatures", fCoinControlFeatures);
            Q_EMIT coinControlFeaturesChanged(fCoinControlFeatures);
            break;
        case DatabaseCache:
            if (settings.value("nDatabaseCache") != value) {
                settings.setValue("nDatabaseCache", value);
                setRestartRequired(true);
            }
            break;