Applications sometimes reopen at start-up in Mountain Lion
Here are a few places to check:


"Under the hood" locations:


Be careful when working with the plist files in the folders listed below. Some of them may be full programs, others may be "helper apps".
Don't touch any plist files for programs you use that may have "behind-the-scenes" assets.
If the plist filename is ambiguous, you can look inside the plist files for the name of the application. If there are remnants from old programs you have uninstalled or were before upgrade, move the file(s) in question to your desktop one folder at a time (/Library/StartupItems), then reboot.
If your system works as expected (meaning nothing catastrophic happens and the program you were trying to kill is gone), throw the plist files on your desktop away, then proceed to the next folder and repeat the process.
When working with files in the Library folders, you may need to authenticate deletes as an administrator.
/Library/StartupItems
~/Library/StartupItems (if it exists)
/Library/LaunchDaemons
/Library/LaunchAgents
~/Library/LaunchAgents (if it exists)

System Preferences: Take a look at Users &amp; Groups in your System Preferences and click on the Login Items button at the top of the window. Check if any programs that automatically load after reboot are on the list and set to run at login.


While there may be other ways to clean house, including formatting your hard dive and a fresh install of Mountain Lion (Check out Lion Diskmaker for a thumb drive installer for 10.8), these will give you a good start.

Happy cleaning!