I'm sure it isn't Adobe Reader 9, it's something MS did because I installed Quicktime on another windows 7 that I had put on another PC and the install worked flawlessly. I installed dozens of applications before Quicktime (some heavy ones like visual studio,
vmware, office, jdk, eclipse, premiere cs4) including Acrobat 9 that was the first I installed and none of them gave this issue. This issue started appearing 3 days ago as the boom of posts about that issue started the 18th of january proves, I've had the
Windows 7 7000 build installed on the other PC since it was leaked almost 3 weeks ago and I never had this issue there, most likely because that PC wasn't connected to the internet during that time.
Check in your Windows Update history what was installed just before you started seeing this.