For heavens sake, just run the McAfee uninstaller.
It will take less time out of your life than the time spent reading the replies in this thread.
If there is still a problem, try a complete removal of Avast (from add/remove programs, then run the uninstall utility, then reboot and install from a new installation file).
If there are still problems after that, then come back with the problem.
All this talk about the numbers of happy users is just a red herring. (But there are a lot.)