Possible solutions for issues arising when two people are editing the same node in parallel:

Who Else Is In Here?
* Notify the user of how many other clients are currently editing the node.  Or what users. 

This is a good social solution.  That works well in small groups.  In large groups, frequently updated nodes will still suffer, but that sort of constant updating is a sign that the content is too large and merits fragmenting.

Last One In Does the Merge:

* When an Editor page is pulled down for the Node, a modification time is embedded in the form, in a hidden input.
* When an edit is posted, if the mod time doesn't match the old mod time, a conflict has been detected.  All changes since the modification time are pulled and merged with the posted changes, then returned to the editor, with an updated modification time.
* The user is expected to review the merge and post the merged changes.

This is a sophisticated technical solution requiring further improvements to the difference engine, and some way of annotating variance in an overlap.

To the Fastest, the Spoils:
* As with LOIDtM, a mod-time is embedded in the editor form. 
* When the edit is posted, if the mod time does not match the old mod time, a conflict has been detected, as before.
* Conflicts are signalled to conflicting users by returning them to the editor, with the latest version of the web page in the input box, and their proposed version in text below the input.  They are expected to merge the two.

Combined with WEIIH, this combines social notification with optimistic locking.  People know they would have stomped when they opened the editor, in most cases, and simply shouldn't have done it.
