Read-Only Participants -
The creator of a wave can now change other participants on the wave between full access and read-only by clicking on their picture at the top of the wave panel, and selecting the access level in the drop-down:
As the name implies, read-only participants are prevented from making any changes to the wave, including adding new participants. They can, however, view live changes to the wave, and look at the history in playback.
You can make entire groups read-only as well, including the "public" group, which includes all Google Wave users. Note that individual permissions take precedence over group permissions, so even if a group has full access, an individual can be given read-only access, and vice versa.
Restore from Playback
Anyone with full access to a wave can now restore that wave to any previous state visible in playback:
Restoring does not delete anything from the playback history, but adds the restored state to the end of the history. That way you can use the new restore function to correct mistakes you or others make in a wave (including restoring the the wrong state!).
New features: Read-only and Restore - Google Wave Blog
