Over at the Geni.com blog they have a new announcement about revisions. There are two types of revisions available Profile and Tree.

Profile revisions

Every time someone adds, edits, or merges a profile, a revision story is created. Profile edit stories even indicate which fields were modified. The revisions tab on each profile lists the revisions stories for that profile.

Tree revisions
When viewing a tree, you'll see an icon on nodes with recent revisions. By default, you'll see revisions from the last 14 days. You can change the time period or hide the icon in your tree preferences.