The current set-up for linking content to a campaign (using macros and the 'Mailchimp campaign' Input format) is great, and seems to work well.
Initially, while using it I found that I had problems producing good output.
I make use of an admin theme in addition to my site's main (client facing) theme. When the content is built for insertion into a campaign, the default node.tpl.php template files are used from my admin theme, rather than my site's main theme.
This is partly good, because it means I can define a different set of templates for newsletter content - but ideally I think there should be a specific set of phptemplate files available from each site's main theme.
mailchimp.tpl.php mailchimp--<node>.tpl.php mailchimp--<node>-<mailchimp-template>.tpl.php mailchimp--<node>-<mailchimp-template>-<mailchimp-content-area>.tpl.php
Does this already exist, and if not could be added as a feature?