I've seen this problem since we started using 9.0.1. When trying to upgrade a client, the installer will become unresponsive. Looking at Task Manager, I will see 3 instances of the Windows Installer. I have left this for up to a half hour so I'm fairly certain this is not just me being impatient.
We are running Windows 7 64, min 8 GB memory. Going from 9,0,1 FP6 to FP8 or FP9.
Any help would be appreciated.