http://www.youtube.com/watch?v=v_UyVmITiYQ&eurl=http%3A%2F%2Fwave.google...
(See from about 31:00 onwards for the relevant bit...)
Real-time collaborative editing. Scroll back and forth through history, showing changes by a single user or of a single paragraph. Embedded comments updated in real time. Edit from multiple clients.
Could we please have all of this? This is several orders of magnitude better than MediaWiki's collaborative editing features.
Steve