I'm testing Confluence 6.0.x heavily, since I (and my company) am really looking forward to use the concurrent editing feature.
I have to say though that there is one small thing that will most likely keep me from updating to 6.x and that is the Discard everyone's changes option when the first editor chooses to close the page without publishing it. It even reaches that far:
Editor A and B are working on the same page. A closes the page without publishing it, but clicks Keep draft. If A starts editing the page again, the draft is there, everything is OK. If, on the other hand, B closes the page and selects Discard everyone's changes, this will alter A's draft as well, removing everything A has worked on.
There should at least be a way (or automatism) for all other concurrent editors to save their work or either some sort of a voting mechanism.
There will be nothing more frustrating than working heavily on a page and then get the own work "destroyed" (accidentally or on purpose, doesn't matter) by another person.
I already expressed my concern about this way of doing it while Confluence 6.0 was still in EAP, but sadly you did not listen (at all).
So... to set Collaborative editing as the new feature of all features (which it is... IMHO), PLEASE, for gods sake, rework the way changes are discarded!