File this under "It goes without saying," but this one had me so puzzled for a time that I thought it bore repeating.
In general, a good best practice for any Drupal site is to put all third-party modules under your sites/all/modules directory; this makes for good portability when it comes time to upgrade the Drupal core, and makes it generally easier to keep track of what you've installed.
I have been banging my head against a problem that has to do with passing FileMaker timestamp data to Drupal CCK date fields. Then, Andy alerted me to this post. So, it turns out that CCK date fields are stored in UTC format, which explains the -5 hrs time offset I was getting. Note this is not a Drupal config issue, ergo time wasted in wrong tree.
I was writing a module to conditionally hide a fieldset on a CCK node editing form based on whether the user is logged in or not, and for a while I was very puzzled as to why my custom module's implementation of hook_form_alter wasn't seeing any of the fieldsets defined by the CCK fieldgroup module.
I searched Google for the terms 'cck fieldset hook_form_alter', which led me to a helpful tip from Benjamin Melançon: