With new versions of the product come new KB articles, make sure to take a look at this as you begin Outlook 2007 development... 

929592 Known issues with developing Office Outlook 2007 form regions
http://support.microsoft.com/default.aspx?scid=kb;EN-US;929592

929593 The known issues with the Microsoft Office Outlook 2007 object model
http://support.microsoft.com/default.aspx?scid=kb;EN-US;929593

Update 1-15-2007...

Here is another KB article related to Outlook 2007 development...

929591 Known issues in Office Outlook 2007 when you use custom forms that were created by using earlier versions of Outlook
http://support.microsoft.com/default.aspx?scid=kb;EN-US;929591

Update 1-17-2007...

Here is another...

929590 Known issues with the Office Outlook 2007 development platform
http://support.microsoft.com/default.aspx?scid=kb;EN-US;929590