I still advocate Repairing Permissions (with Apple's Disk Utility) before AND after any system update or upgrade, as well as before AND after installing any software that requires an installer that asks for your password.
I have seen software installations go sour because the installer did not find everything as and where it should be.
I have also seen software installations go bad because the installer did not clean up after itself properly and did not leave everything as and where it should be.
This is just my own personal opinion and practice based on my own observations. Others may disagree and that's OK. I can only base my routines and my advice to others on my own experience and conclusion. I don't pretend to know why others believe otherwise.
Repairing Permissions after the fact (i. e. not immediately before and after an install) may NOT help. Try it anyway, though.
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Additionally, if your machine does not run 24/7 so that it runs the daily, weekly and monthly Cron Scripts in the middle of the night as intended by Apple, run Cocktail (shareware) as well.
Cron Scripts are maintenance routines designed by Apple to run on a daily, weekly and monthly basis in the middle of the night.
If you don't run them, you WILL run into trouble, sooner rather than later.
Here's an excerpt from the Apple tech doc <
http://docs.info.apple.com/article.html?artnum=107388>
Mac OS X performs background maintenance tasks at certain times if the computer is not in sleep mode. If your computer is shut down or in sleep at the designated times, the maintenance does not occur. In that case, you may want or need to run these manually.
Mac OS X periodically runs background tasks that, in part, remove system files that are no longer needed. This includes purging older information from log files or deleting certain temporary items. These tasks do not run if the computer is shut down or in sleep mode. If the tasks do not run, it is possible that certain log files (such as system.log) may become very large.
Also, from: <
http://docs.info.apple.com/article.html?artnum=106978>
The disk activity generated by find is a normal part of file system maintenance, used for tasks such as removing invisible temporary files that are used by the system. It is scheduled to occur early in the morning at 03:15 everyday, 04:30 on Saturdays, and 05:30 on the first day of each month.
NOTE: There have been comments to the effect that Apple "fixed" this in 10.4.2 and later versions of the OS, but I have not been able to verify this to my satisfaction. The reference in the 10.4.2 release notes are far from explicit on this subject.
Other, more reliable reports indicate that this seems to have been fixed in the current version of Leopard.
In any event, Repairing Permissions and/or running the Cron Scripts cannot hurt.
If you have DiskWarrior, run it regularly too.