Campaign Monitor is a great tool for email marketing, particularly when using the Custom Fields feature.Custom fields can be used for all sorts of purposes, for example, you can create a Topics of Interest field to allow subscribers to nominate what interests them most.
Using your Campaign Monitor account you can create segments to send certain campaigns only to those subscribers who have a specific interest.
One of the features Campaign Monitor has implemented is the ability to export and re-import your subscriber lists complete with custom fields. So this means you can export a list, make any necessary changes to the custom fields in Excel, and then re-import to update the custom field values. A lot quicker than trying to update records one by one.