I encountered the black screen also. I started UserAgentTool from the command line and the following messages were reported:

file:///opt/userAgentTool/qml/main.qml:1:1: module "QtQuick" is not installed
import QtQuick 1.1

A search of talk.maemo.org turned up the following post:
http://talk.maemo.org/showpost.php?p...8&postcount=72
from which I understand that UserAgentTool may have a dependency on a version of QtQuick which is only available in the CSSU.

Would it be possible for you to build UserAgentTool to use the stock Maemo PR1.3 version of QtQuick?

Many thanks for your work on what is surely a very useful application.