Book now, Liz. If you cancel before penalty face, you loose very little, if anything.
I follow my wise travel agent's advice (her name begins with an N) to book early so that you get the cabin and cruise that you want.
In fact, Alan and I just added Sydney to San Francisco on the Navigator for 2010. Too good to pass up.
One more edit, if you can go, don't put trips off. Who knows what can happen during the year that you wait. People get sick, bad things happen, go while you can.
