I have a Salesforce trial account.
In the Outlook Configuration section (Administration Setup/Desktop Administration/Outlook Configuration), I created a custom fields mapping between Outlook fields and salesforce fields.
Everything is working as expected, except for the Outlook ManagerName field. When selecting that field, I can only map to a predefined set of Salesforce build-in field (as shown on the Image), but not on a custom field I defined on the Contact object.
Note: For all other Outlook fields, the list contains all build-in and custom fields defined on the Contact object.