We've had a couple clients recently have some trouble with some of the items that are hidden at the bottom of a Drupal node edit form.  Depending on what modules you've got enabled and what content type you are editing there can be a lot of fields that you have to generate in order to create a node.  So to help with usability Drupal 5 hides many of the fields by logical groups.  Unfortunately, if you don't know what logical group you're looking for you can no longer quickly scan down the page to find the reference you're searching for.   I have yet to see an expand all feature that works to quickly expand all hidden groups within a drupal web form, however, perhaps this will be added in Drupal 7 as more usability enhancements are contributed.  

The first problem that we had was that a couple of our clients were adding old information and trying to figure out why stories/blogs that were from 2007 were showing up ahead of some of the items posted in 2008 in a category (taxonomy). Taxonomies are generally ordered by date or alphabetically and in this case the editor hadn't changed the "Authored on:" field to reflect 2007 and so it kept the default time it was entered on (in this case 2008). I'm not certain if it was just that the editor didn't think to look under the "Authoring information" group or if they didn't where the date logic was inserted, but it as a simple matter to train the user on were to change this.

The other issue that we ran into had to do with the access control permissions not being clear enough to allow an admin to easily know why the Publishing options group was invisible for some users but not for others. The administer nodes module was the relevant permission that needed to be turned on, but there isn't a list of what the effect of these permissions is. It would be great if somewhere there was a list of what these permissions did, written in a way that a user would understand.