If you want to use it:
1. Download the Qt4 squashfs package and put it in /mnt/card/ or somewhere.
2. Install squashfs utils from the pdaXrom unstable feed.
3. Edit /etc/profile and modify the line specifying the QTDIR to
4. Make sure that the directory /usr/local/qt exists and it's empty.
5. Before running a Qt app, mount the squashfs image, if you want to do this automatically edit your startkde or startx file, whichever you use to start X, and at the beginning insert the following line
mount -t squashfs - o loop /mnt/card/qt-4.0.1.squashfs /usr/local/qt
And now you will use Qt4 in X.
I don't see any practical reason for it currently. I just worked with it because Qt4 was supposed to include the Qt UIM immodule but it doesn't, so Japanese input doesn't work in Qt.
But since I made it, maybe someone will find use for it.