I own a few websites and Alexa is known to be completely inaccurate. I wouldn't rely on that info because they don't have access to website analytics. Only the owners of websites with access to that information know for sure. Per the conference call unique users per month continues to trend up, which is the most important thing to pay attention to. Zillow has already achieved critical mass with it's website, meaning it's the destination of choice for home hunters and therefore RE agents.
Zillow's ranking has now dropped from 107 to 116, so this stock is definitely going lower. Especially when Congress partially or fully removes the mortgage deduction from the average homeowner. Then watch interest in housing drop like a rock. Congress will most likely do this in early 2013, if not sooner.