In order, the four that bother me the most:
1) System Restore:
This one can kill a flight sim installation quicker than anything will. That's not all, it's a darn good way to lose pictures, videos, and anything else you might want to save on a computer. Then again it's hard to beat, if you develop a severe problem with your operating system.
By default, "Windows" will enable "System Restore" for every partition, on every hard drive. This includes external hard drives.
I would strongly suggest disabling "System Restore" on all partitions, on all hard drives, except the one that "Windows", itself, is installed on. On most computers, this would be the "C:" drive.
2) Automatic Updates:
This sounds like a good idea, but it has probably caused me as much grief as anything else. "Windows" updates, driver updates, software updates, and even "addon" updates have all caused issues. "Adobe Updater" once did me the great favor of installing "Adobe AIR". That killed FSX until I "uninstalled" it. It seemed "Adobe AIR" wouldn't allow FSX to access ".air" files.
Automatic Updates WILL cause more headaches than they will relieve. Turn it off on everthing!
3) Antivirus Programs:
I haven't had one these programs cause any trouble, at all, for about six years! It's not because they are so much better than they used to be. It's because I haven't used one for that long! I also haven't had any worms, Trojans or viruses in that period of time.
This one is strictly up to the user, but I'm much more comfortable without it.
It's hard to argue against "installers". They are great for installing the proper files, to the proper locations, if the "assembler" didn't make any mistakes. The problem is more with the "uninstall" process that often may remove important files that were "overwritten" during the "install" process.
My biggest problem with "installers" is that they seem so "over used". I always try to avoid installing scenery, or aircraft, directly to the simulator. This requires a bit of time and effort, but is well worth it. If done properly, you can avoid running those "installers" ever again, in most instances.
I am working on several guides to post on my website, that will help resolve many issues related to Flight Simulator X.
Please keep checking back, and leave a comment if you feel like it. I could use some ideas!
See ya, Milt