I think it would be really great to be able to segment using multiple list membership parameters. For example. When we have an event we would like to redact current attendees from a promotional email to our newsletter list so that people who are registered do not also get the email.
I realize you can do that manually by creating a new contact list and removing contacts from that list by selecting them through the list you want to redact but it's cumbersome and it doesn't allow for the most recent information when scheduling an email. So if someone registers for an event (and the event registration contact list automatically updates when they happens because of integrations) between when the email is scheduled and sent they won't receive the email.
Seems that with the introduction of segmentation this would be a pretty hand feature.