Try switching to PV2012, you are proably in pv2010.
To be clear in LR4.0 there is a Moiré in the develop module when you click on the adjustment brush at the top right. In LR4.1RC the Moiré option is missing. I'm guessing tis is a bug and that Adobe didn't intentionally remove it.
Thanks RIch! Yes, I had PV2010 set and if I toggle the image to PV2012 than the Moiré brush appears. Way cool! Thanks!