Depending on the type of ads being served that cross-profile-pollination could lead to info leakage and problematic and/or weird situations. It makes me want to be able to build a fake persona rather than a ghost/anonymous profile
I'm not sure who gets the worst deal from tracking, the companies buying ads or us having to see them.
That said, I have heard a few times comments mentioning that it's easy to filter out (from the ad provider side.) I hope not, but if it is, I would only hope someone smarter than I would send a PR. :)