This could get interesting. Mozilla - maker of Firefox Internet browser - dropped this very idea not too long ago. Well, looks like the option is back on the table.
What the DVR has been to TV commercials, this built-in option could be to online ads. Where TV commercials are a static entity, online ads can follow (track) you around the information superhighway, making them more targeted to what you like or would be willing to buy. There are 3rd-party tools out there that do what Mozilla is contemplating, but if you're an average Internet user, those tools may as well not exist. But build them into a browser? Totally different story.
There may also be unintended implications for parents using browser history to track their kids' usage, but that can probably be easily remedied.
From a business perspective - this could be a game-changer on the net. If sites can't make money using targeted ads, then they'll need to develop other revenue streams. That could lead to a whole new philosophy for sites that rely on ads to make their living. Charge for materials that were once free? Change a subscription fee? Require ads to have access to your browsing on their particular site? Not going to be an easy solution, whatever it may be.
Like I said... interesting.