VSTO offers developers an opportunity to create applications within Office. Although there is not much around (yet!) except from Microsoft itself, I really think VSTO is a way to really improve productivity for Information Workers. John R. Durant, which is one of my favorite Office bloggers, wrote an article on MSDN about an Outlook Business Contact Assistant add-in. I think this arcticle is a good way to start your way into VSTO.
The Business Contact Assistant
“Learn to use Microsoft Visual Studio 2005 Tools for the Microsoft Office System to create a managed add-in for Microsoft Office Outlook 2003. This add-in creates associations between contacts and Inbox items, and reports on Inbox activity in a user's contacts list. You use the development tools and programmable aspects of Outlook 2003.“
Read the complete MSDN article