If you have seen the error below when using objects from OOM in .NET 2.0 code then the information that Mason posted recently will explain a lot.  The key to avoiding this error is to use the interfaces in OOM not the CoClasses.  Mason explains why in his post...

Unable to cast COM object of type 'System.__ComObject' to class type 'Microsoft.Office.Interop.Outlook.MailItemClass'