I think that this experiment has very little room for error. For example, if A writes "The quick brown fox jumped over the lazy dog" and B sees it the next day, that is very good proof of shared dreaming. I could not possibly fudge the results, but the participants might, by PMing and discussing what to write. I think that there should be admin/moderator supervisation of this thing. If that can be done, this is a great experiment!

P.S. I have devised a SURE way to have a FAKE shared dream. You and a friend write a script of what will happen, memorize everybody's lines, and go to sleep at the same time. Then say what you should say and control the DC's the way you are supposed to be, and bingo, a shared dream.