Back home
Yesterday I got back home from Redmond (after about 20 hours).
Microsoft Office System Developers conference was a blast - sessions were great; mostly I was listening to the client track session (VSTO stuff).
I also attended SDR event, which was held one day before the conference (on Monday).
As you already know, VSTO v3 CTP was announced and you can download it here; you will need Office 2007 beta1 Tech Refresh (you can get the beta if you're in beta program) and VS2005. New CTP has some features that work against new capabilities in Office 2007 - you can check the CTP tutorial. Also, Kathleen has posted a video on how to create a custom task pane.
VSTO team has done some extensive plumbing work so that the new VSTO runtime is more strengthened. They have also added support for application level add-ins for other Office programs. There is also a support for application level custom panes, ribbon (no designer yet) and custom form regions for Outlook. Object model for Outlook is enhanced - the existing APIs are unified. Primary customization technology are still add-ins and from regions. Some new events are also added which will make your life easier (customization of context menu on items, folders, views, attachments).
Ribbon customization for Office 2007 programs is done via add-ins or with new Open XML format you can simply add your customization to the document. You can use the XSD ribbon schema (again, only if you're in Office 2007 beta) to start playing with ribbon. Maybe one disadvantage is that you can't add controls to the ribbon at runtime (the XML customization is loaded when application starts). You can read more about UI customization in these two articles.