The tracking of browsing is something I spent a long time agonizing about, especially also given our experiences at Root Markets back in 2006 with Root Vaults / AttentionTrust etc. An interesting failed experiment to write about at some point. Anyway we decided to switch to letting users just tip sites they like without doing an allocation model based on traffic. This is a new change for us but I think there will be room for a bunch of different models depending on what users are comfortable with. We also took pains with our other product, optimalblock.com for iOS to make sure that we will never use or share individual level-data, and wrote that into the privacy policy. It will limit our ability to pursue other revenue models but that's key in this space I think.