I find secondary contacts quite useful but limited. I would like the option to add some notes at a minimum if that can be developed into 2012 - great!
Also, when promoting a secondary contact, I would prefer to leave the history of that (now primary) contact within the initial primary contact so the database stay tier together.
I think it is great that ACT! allows a search of this field. I wish the secondary contact name would also show in the list view page along with the primary contact. I don't even think I can customize the columns in this view as the field "secondary contact" does not appear in the drop down list for selection.