Is an opt-in ad network feasible?

I think it's safe to say ads are necessary for many publishers. The subscription model has it's limitations. Ads are a necessary evil as I see it.

What if you could opt into certain topics for ads that followed you around the web - no matter the platform - based on something ever present like the social graph? I'm talking PC/mobile/game console/E-reader.

Would people go for this idea and actively sign up?

Would this provide to be financially feasible for advertisers?

It's just an idea that popped into my head so please be brutal. I think Adwords is a bit broken and could use some retooling.

Re-marketing is essentially opt-in advertising since it's based on browsing choices to explore the brand or product.

I think Facebook page 'liking' is essentially this except that it's restrained to the boundaries of Facebook.