Google Groups is one of the services that would benefit a lot from an integration with Google Calendar, Google Docs, Google Sites and other Google apps. It makes sense to create a document and to collaborate with other group members or to create a calendar and share it with your group.
Google blog announced that the integration is already available. "As an example, imagine you're organizing a local intramural softball team tournament. You use Google Docs to keep track of the rosters for each team as well as each team's performance. You want all the players, but only the players, to have editing access. You already have a Google Group set up with the tournament participants, so you simply share the spreadsheet with the group itself, granting the group members permission to edit."
To share a document, a calendar or a site, use the group's email address (email@example.com) in the sharing dialog.
And if you want to unsubscribe from a group, Gmail makes it easier by adding an "unsubscribe" option when you click on "show options".