They will probably offer it free if... (Score 1)

Not only can I imagine such a device. I imagine them offering it for free as long as they are able to track your Internet usage for each individual computer. (For creating "aggregate" data, of course.) Personally, I long for the day when I'm no longer served ads based on my husband's interest in football stats. I'm also sure he no longer wishes to receive ads based on my interest in Anime. ("Stay off my computer, you're messing up my Google Desktop feeds!")