One of the nicer features of Outlook 2007 is the way it neatly groups your messages by date or other criteria, but it's not always easy to see at a glance. There's a little-known option buried in the settings that will shade the group headings to make them more easy to distinguish.

Here's the default view, notice how your eyes just brush right over the "Yesterday" without really noticing it.

To change this setting, go to View \ Current View \ Customize Current View and then click the "Other Settings" button.

In this dialog you'll find the "Shade group headings" option, which you'll need to check. Note that this is a global setting across all views, not just the current one.

The change should be instant, you will now see the darkened group headings.

I find this much easier to work with than the default setting, although it's not quite as "pretty".

Note: For Outlook 2003, you'll need to use View > Arrange By > Current View > Customize View: Messages. Thanks Jon!