I ran into an issue where I was not able to use the Localization update module in Drupal on an Acquia hosted site. This is because the default location where the module stores translation files, sites/all/translations could not be created due to this directory being write protected. I suppse write protecting any directory location that could contain executable code is a good practice.
This is an odd one. I had a Drupal site, which when I tried to rename a menu link, would revert to using the title of the destination page instead of the text I entered for the title. For example, I have a Apachesolr search page that allows you to search for users on the site. When you are on the page, the title appears as "Search Results." Nothing unusual there. But, I wanted the menu item that allows users to get to the page to use the text "Member Directory." However, after saving the menu link, the text reverted to using "Search Results" in the menu instead of "Member Directory"
A good reason to remove inactive modules: drupal_system_listing(). In some recent on a Drupal 7 site, I kept noticing errors when running database updates via drush, which looked something like this: