Myths of required versus not required maintenance for Mac OS X

Question

Many people come in here claiming to have run maintenance scripts and other addons thinking they are doing a good thing for their computer. Turns out Mac OS X requires very little basic maintenance. Here is a true false listing of maintenance that Mac OS X requires:
1. Backing up your data. True. Definitely required unless you don't value your data, or wish to spend thousands on data recovery when your hard drive fails, or when you make a mistake about deleting a file that you shouldn't have.
2. Repairing permissions. Partially false. Most times it isn't required. Occasionally though it has been discovered that after a system is updated with new security or new operating system update, that issues disappear when permissions are repaired via Applications -> Utilities -> Disk Utility.
3. Repairing the directory. Partially false. Only required if your data is backed up, and access to your files suddenly is limited even after Spotlight indexing is complete. More true if you get a flashing ? disk, though zapping the PRAM sometimes fixes this issue as well.
4. Deleting cache files. False. Corrupted cache files can create more harm than good, but system maintenance utilities which attempt to delete those files frequently do it when some system applications are running, creating additional corrupted cache files. If you suspect corrupt cache files, often only restoring your backup will fix those issues. If you must try to fix corrupted cache files, backup your data first.
5. Updating prebinding. Partially false. Some applications may not launch properly if their update doesn't update prebinding in the process. Some Mac OS X system updates do updating prebinding when they are optimizing the system. Other times permissions, cache, preference, or incompatibility issues can cause applications not to launch. Backup your data before attempting.
6. Keeping your system not overflowing with data. True. Check your capacity of your system hard drive, and how much space is used. If over 85% is used, it has been arbitrarily found that the system may slow down. Deleting unessential files can help. Ask here what those are.
7. Logfile cleanup. True. Required at least once a month. Some third party utilities will do this manually whenever you choose. It can also be done by the operating system if your system is allowed to run in Screen Saver instead of Energy Saver overnight.
8. Spyware and virus cleanup. True to an extent. While there are no viruses in the wild as of the writing of this article for Mac OS X applications, if you share data with Windows users, you wouldn't want to become the Typhoid Mary affecting those users. Vigilence in understanding that you shouldn't open attachments from unknown e-mail sources and not falling pray to attempted identity information gathering by e-mail is always wise. If uncertain about a source, contact them first to find out if an e-mail really was sent with an e-mail, snail mail, or phone call sent to their known address, and not an e-mail replying to the message you received! The latter may be spoofed.
Mac OS X security updates will keep you even safer, though sometimes a system update is required to get them. Basic good security practices though are always recommended, even if you can't apply those updates, in event your application that you can afford isn't yet updated for the new system.

Answer 1

It is not strictly true that there are no viruses for Mac OS X applications. MS Office applications are Mac OS X applications, as are OpenOffice etc., and my understanding is that Word documents etc. can introduce macro viruses. Even though these may not be able to do the harm they would do on a PC, I believe they can do things such as infecting other documents, templates etc.
Given the number of users who are now also running Windows on their Macs via BootCamp or what have you, should a note about vulnerability to Windows viruses in such cases be added? It sounds otherwise as though only non-Mac Windows users are vulnerable.
- cfr