I spoke to the nice women in the booking office today about the priority stuff. They told me that at the moment, bookings officially open on 4th October for 2011. However, they are expecting a date before that to be announced for members but at the moment there's no news as to when that will be but members should (that's should - not will be) notified. Whether existing members count or whether it's just for those in the new schemes, nobody seems to know (for instance, my current membership expires in October so she wasn't sure if I'd be given priority booking this year or not - in spite of being loyal for the last ten years.)
The suggestion was that I should send my booking order in with my membership renewal. We shall see.