The interesting thing to watch about AV is not so much who voters will give their second preference to, but rather whether they'll change their first preference.
In other words, how many people are currently voting Labour because that's the largest anyone-but-a-Tory party, and how many were voting Tory to kick out Labour? Will these people now start voting Green, or UKIP, or LibDem, and just vote Labour/Conservative with their last-but-one preference?