as more of a type of brand-tracking measure than trying to attribute it directly to ads. Most people look at the number of stories that are created and sentiment is a good measure. If you see the buzz about your brand changing significantly there's something happening with your brand. But what was the change that led to that and can you attribute it to one particular thing. How do you incorporate it into media-mix models? Its not just the number of stories told, what matters is their reach and frequency and resonance and if they impact people's behaviour. As consumers become more knowledgeable about the commercial value of their data, do you foresee privacy issues growing? Privacy is obviously a sticky issue for consumers. We're trying to be very up-front about the way that privacy works on Facebook and get users increasingly to really understand privacy. I know from my kids, who use Facebook -- they know the privacy settings very well, and I think that we'll see more and more that people are going to embrace the understanding and the use of privacy. This is not about Facebook, this is overall -- privacy is something they're going to understand and take more control of themselves. Do you believe social media usage will continue to grow? One way to think about growth is the number of people that engage with a social media site -- that's growing. The amount of time people spend on Facebook continues to grow as well.