Mat Newman’s tip about a clever use of categories reminds me of another useful but little-known feature.  First, put the focus on a document in a view (click once on it.)  Now hold down the control key and click on another view or folder where that document also exists. The view will be opened with the focus on that same document rather than where it was the last time the view was opened.  One example of how this is useful is if you want to see other documents that are related and appear near the document in the other view.  For example, in your mail file, find a document in the All Documents view.  Now hold down the control key and click on the folder where it is filed.  Another valuable effect is that if the document doesn’t exist in the second view, the view will be opened in the same place it was when last opened, so you can tell that the document doesn’t exist in the view.

Another place that this used to be helpful was in the help files.  If you found a topic in a search, you could switch to the Table of Contents view and it would jump to that same document so you could read all the related documents in the chapter.  Unfortunately, that broke with the new navigation format of Help.