From Signal vs. Noise:
We've recently added a few more "quick hit" demo videos to the Backpack tour. These tutorials show how easy it is add users to your Backpack account and share pages with them:
Video: Add others to your Backpack account
"Backpack excels when you use it with other people. Add co-workers, colleagues, friends, or family to your account and share pages, knowledge, files, calendars, reminders, and more."
Video: How to share Backpack pages with colleagues and friends
"Backpack makes it easy to share a page of information that you've created. People you share with can also add new items and change content on the page. It's perfect for quick collaboration or sharing knowledge."
And this video answers a question we get a lot...
Video: How to get your Basecamp Milestones into your Backpack Calendar
A FAQ from people who use both Basecamp and Backpack is "How do I get my Basecamp milestones to integrate with my Backpack Calendar?" The answer: By adding the Milestones iCal feed into your Backpack calendar. This video shows you how. More details here.