apps are not installing after Debconf window appears when download is complete & software gets ready to be installed in ubuntu software centre!
I was experiencing the same problem. My application install hung for about 15 minutes with the Debconf window open. Eventually I searched the web for a solution. Just after seeing this question posted the Debconf window closed and the installation proceeded to finish. I'm not sure why it took so long, but it seemed to be doing something. I'd recommend waiting to see what happens as long as the system responds to mouse moves. If the system hangs the mouse will not move.