Just traded in our car today for a 2 year old car, wasn't planned, but spotted it on dealer's website and was a very good deal, car exactly what we wanted. We were going to trade in next summer. As luck would have it, the motor tax expires 31st December so we can renew for 2012 at €156, doing this on monday. At least won't have to pay the old car tax of €333.
Prior to getting that trade in, we sent in payment and form for motor tax renewal for the old car, chancing our arm, just got letter back today saying can't tax it in advance for 2012.