Hello there
I just stumbled on this:
Using Outlook 2007 my yearly appointments (birthdays, etc) have suddenly turned into 12-yearly.

This seems to be an issue with Outlook'07 as mentioned in this thread:
(I'm a newbie, so i can't post links. Please copy and paste...)
social.microsoft.com/Forums/en-US/windowsmobilehelp/thread/8dbfde6c-9788-4ff9-a4b8-6b5751b765da
Sorry, found no workaround or solution (apart from apparently adding a specific time to the app and not just all da) , but just wanted to warn you and any ideas would of course be appreciated.
Cheers
bern viking