What is it?
Tree merging will allow you to claim a profile in more than one tree. If others nodes in the merged trees are duplicated, you will be able to merge these nodes, creating one combined, accurate record of your genealogy using the information in each tree.
It basically give the means to join currently separate Geni trees into a larger tree. (In the future, you will be able to use the GEDCOM import feature to merge your GEDCOM data into an existing family tree on Geni.)
Before Tree Merging, you will be able to merge any two nodes in your Forest (assuming you have the requisite privacy permissions for the nodes). You'll be able to merge two unclaimed profiles, or else a claimed profile and an unclaimed profile. Geni will choose which one to keep based first on whether one is claimed; if not, then the more-complete profile (per Geni's profile completeness bar) will be chosen. In the event of a tie (likely for two new profiles), the user's input will take precedence (did you drop A onto B, or B onto A?)
Once the profiles are merged, the secondary profile will be accessible from the profile page of the primary but none of the profile data will be merged yet. The merge can be undone at any time until the user clicks the "Automerge" link on the secondary profile, at which time Geni will automatically merge whatever we can (initially photos, guest book comments, email addresses, and possibly more) and the merge is considered final. The secondary profile will remain, with only the data that could not be automerged, until it's deleted using a link or button on the secondary profile page.
If there are potentially duplicated relationships you can indicate the additional nodes to be merged. This creates a cascading merge flow until all relevant nodes have been merged. Then each can can be finalized as noted above.
Once profile merging is released, Tree Merging extends this by allowing you two merge your profile with a profile on another tree using a request system for the necessary approval.
Later releases will refine these features and implement more complex ones.
Suggestions and Development
See the discussion page.