Add customers to mail list automatically when they signup
MailChimp, for sure!
I think a big MailChimp integration has to be the excellent segmentation and automations they can provide. Ideally I'd like to see this considered. Having MailChimp handle order notifications, as well as segmenting customers according to their survey preferences would be huge.
I think if Subbly can open up to allow for segmentation and order notifications to be passed through MailChimp it would allow us to level up for marketing purposes. - https://mailchimp.com/features/order-notifications/