Outlook contains a great feature if you bill by the hour or want to see where all of the time in your work day goes. It's called Journal, and it can actually track your work activities not just in Outlook but also Access, Excel, PowerPoint, and Word.
It's not turned on by default, so if you want to start tracking in Outlook 2007, visit the Go menu and select Journal - or just use the convenient keyboard shortcut Control-8 in any version that has this feature. You will most likely see this message:
Click Yes to turn Journal on and then select the activities you want tracked, including appointments, tasks, and your other Office applications:
You'll see a timeline with your activities and you can easily search your journal entries and even add new ones manually if, say, you want to take notes during a phone call or meeting. Just click the Start Timer button to track the length of the interaction.
If you don't set your Journal Options when you turn this feature on or you ever want to modify these settings, in Outlook 2007 go to Tools, Options, and click the Journal Options button on the main Preferences tab to revisit them. In Outlook 2010, use File, Options, Notes and Journal.