Ask people what they want from current services (email is the one 99% will understand) and work out how Wave could be used to meet that need. i.e. Instead of emailing a new attachment everytime a document is changed, tell them to put the text in the email and how they can continue to edit it.

Does anybody know how Wave is going to deal with Spam? I assume you are not limited to sending waves to people who have added you as a friend or contact.