Well first the bad news in that it's not a new object model but that's not surprising when do they rewrite any Office code. But it has been greatly enhanced with over 70 new objects and numerous enhancements to the existing ones. Ok now you've triggered my interest.

With VSTO 3.0 we'll be able to write managed add ins that cover the functionality of CDO, MAPI, and extended MAPI.

This trusted Add-In will be the primary customisation model. As it will be the Add-In that is trusted and not MSCOREE.DLL. by doing this it should remove all the security prompts that we love to hate as there will be no seperate trust and security models. Things like address lists that were previously only available in CDO will now be available as part of the object model.

It will still return weekly typed message objects that will still need to be casted into appointment/message objects as needed.

Context menu items will now expose events that can be captured and overriden.

A new PropertyAccessor object will provide access to MAPI properties and you will be able to Get/Set custom properties.

Outlook forms currently look very dated and run VB script. Forms can now use Add-In technology and are deployed via the registry and saved form files. They now support themes and provide full event handler support.

One interesting object was the new table object that provides a lightweight read only object that you can use to iterate over large numbers of folders.

Searching has been improved by using a content indexer to search for items.

I still think they have a problem with multiple add-ins though as what happens when two add-ins respond to the item save event???? who knows and they don't appear to care to much either so maybe I'm worrying about nothing.