Custom fields for user's profile
From AbleCommerce Wiki
AbleCommerce 7.0 has the back end support that Merchant could store customer information for a user that only the merchant would update on the user's/customer's profile. .. ie.. an account number, special note, cross-reference to another user, etc.
There is a User.Settings property, which connects to a UserSettingsCollection class. The data here is persisted to the database and associated with the user. It would be the natural place for this kind of data.Some one who would like to have custom fields for the customers then he/she just have to build some admin UI to access and work with this field.