Want to know which ones of your ACT! contacts belong to a specific MailChimp list?. That's easy. Launch MailChimp Plug-in for ACT!, go to Actions>Lookup Contacts in a MailChimp List.
As you can see, you can lookup contacts that belong or do not belong to a list or a group of a list.
Contrarily to lookups of results, this operation requires a connection to the MailChimp server as it actually reaches out to the MailChimp server to retrieve the current state of the list.