I'm back from vacation and ready to resolve the bug in my little application with Outlook and OneNote.
To summarize, if a user sets the Outlook startup folder to be sticky notes, then OneNote will not start when Outlook is started. When the user navigates to a new sticky note folder, though, OneNote will start.
I did some investigation into Outlook's object model (on this site: http://msdn2.microsoft.com/en-us/library/bb208225.aspx) and could not find an event for Outlook startup which exposes the folder which gets opened. I did a little investigation into MAPI, but my one line application would easily spin into a much larger application if I went this route.
Then I started thinking about the user who starts to the sticky notes module - there must be a reason for that. Since the setting is deep in the Outlook UI, making a change like that is a deliberate action. In other words, what finally occurred to me, is that whoever changes this setting specifically wants the Outlook sticky notes module opened on start. And if that person wanted OneNote to start instead, he could just as easily launch OneNote.
Based on this line of reasoning, and coupled with the increased amount of development work to change the behavior, I decided to not fix this bug.
Next up: another power toy based on books available from Project Gutenberg (http://www.gutenberg.org).