Years ago, when Gmail was definitely beta, we could create email "lists" (Groups) by pasting a list of email addresses into a text field. Gmail would digest the list and create a Group. Google removed this functionality, perhaps to reduce abuse by spammers. Instead we had to create Groups one member at a time. This was a serious PITA for the various sports teams and organizations I work with.
I gave up hope that Google would ever restore this functionality, but today I discovered they have -- probably in the past few weeks.
It's subtle, but the UI for creating a Group, or adding email addresses to a group, is now an expandable multi-line text box. If you paste in a list of email addresses Google will match them to existing Contacts and add the Contacts to the Group. Failed matches become new email-address-only members.