Why does this matter?
If Tasks are ways of keeping track of things that need to get done, and To-Do's are ways to show that you need to do something about some item some time in the future, do we really need to use both? The short answer is yes.

We do need them both.

Tasks are ideal for planning and managing projects. You can store lots of information in a Task item, and keep track of details in one dedicated spot. To-Do's, on the other hand, are more like sticky notes plastered on pieces of mail or the business card some guy gave you at the party. They are much more free-form, and natural, saying in effect, "Don't forget to look at this again tomorrow" (or next week, or whenever). They feel more informal, and they don't carry all the information that a Task can contain.

You could easily live without To-Do's. Just create a Task for each thing that needs follow up. But for a lot of things, this is time-consuming overkill. Its much easier to tag items with a Follow Up flag than it is to create a new Task & copy the relevant parts of the message into it. I get a message from an old school buddy that I want to remember to reply to. I set the Follow Up flag for next week and boom, I'm done. It's much faster and more natural than creating a Task.

Another reason to use To-Do's is that they appear in the To-Do Bar, a pane that can be visible in every Outlook view. At most, it takes a couple of seconds to expand the To-Do Bar and scan through it for To-Do's that need doing. To-Do's really are convenient.

Recommendation
If you just want to remind yourself that you need to do "something or other" with an Outlook item, set the Follow Up flag and turn it into a To-Do that you'll be able to spot at a glance in the To-Do Bar.

If you are planning some project, or need to record details about something that you need to do, create a Task to track and manage it. Although they can be confusing at first, using Follow Up flags, To-Do's, and the To-Do Bar in addition to Tasks quickly becomes natural and automatic.

Diane Poremsky is the president of CDOLive LLC and a Microsoft Outlook MVP. She's author of Teach Yourself Outlook 2003 in 24 Hours (Sam's, 2003) and coauthor of OneNote 2003 for Windows (Visual QuickStart Guide). For questions or suggestions for future columns, write her at outlook@cdolive.com.