When setting up an email campaign it would be useful as an aid to targeting specific contacts to be able to search user defined fields within the contact. For example when creating an email campaign for machinery User Defined field 1 could be set as 'New', User Defined field 2 could be set as 'Used' etc. so contacts can easily be added to a campaign by searching by the User Defined Fields.
You can now easily setup tags or custom fields on contacts ... and then use these in reports to get lists of contacts... and then add to a campaign from such a list