GoogleWave is still in 'Technical Preview' state and feature development is ongoing and are being added and worked in the background The latest addition is Email Notifications. This will will notify you via email at your selected frequency of any updates to waves. This feature is means that you don't need to logon to the wave to check for new waves or new blips to existing waves.

For more info see the update on the Google Blog at http://googlewave.blogspot.com/2010/03/help-test-email-notifications.html