I've created a custom column on a SharePoint contacts list, but I don't see the data from that column when I link the contacts list to Outlook. Why not?
Each contacts list in a Windows SharePoint Services or Microsoft SharePoint Portal Server 2.0 site displays a Link to Outlook hyperlink. When the user clicks that link and accepts the resulting prompt, Microsoft Office Outlook 2003 creates a read-only replica of the content of the contacts list as an Outlook contacts folder and keeps it up to date. This can be a good solution if you don't want to use an Exchange public folder for workgroup or departmental shared contacts.
However, as you've discovered, custom columns in the SharePoint list don't result in corresponding custom fields in the Outlook contacts folder. The Outlook contacts folder contains data only from columns that are part of the standard schema for a Share-Point contact. The standard File As column and any custom columns aren't represented in Outlook.
You can still get to custom columns from Outlook, though. The Notes field in Outlook contains not only the Notes column from the SharePoint contact, but also a link to the SharePoint contact. To see custom columns, click that link to retrieve the full SharePoint contact from the SharePoint site. You'll see all custom columns and—if you have permission—be able to edit the SharePoint contact (something you can't do from within Outlook 2003).
The 2007 Microsoft Office system will greatly expand integration between SharePoint lists and Outlook folders. In addition to contacts and events lists, Microsoft Office Outlook 2007 will be able to maintain replicas of tasks lists and document libraries, and all folders will support read/write access rather than the read-only access that Outlook 2003 has. However, Outlook 2007 replicas of SharePoint lists still won't support custom columns.