I am guess here, but people affected have not done a clean install but installed over their existing Windows 7 system. In general I would describe doing so as stupid and IMO it should not be allowed. A major OS update should be done fresh and clean. I have not had any issues with updates on the three systems I am having Windows 8 running on. And yes, obviously all three were clean installs.
that a good way to do stuff if you don't know how to maintain your PC properly.
its the cowards way out, i know people that reinstall their OS every time they f-ed up something on their PC, they have no idea how to fix it, and just reinstall.
my main rig was originally installed with Vista, then SP1, then SP2 updated to 7 and then SP1, thought that time i went from Q6600 on nforce to 920 on intel chipset and now 3770k. With zero performance issues.
Server from 2003 to 2003 R2, to 2008 to 2008 R2 and now 2012, and again 3-4 motherboards changes, no reinstalls.
ZERO PERFORMANCE ISSUES.