So, just some context... I always block ads by default. I do however allow ads from sites that I use regularly such as El Reg.
Just putting aside the insidious data issues behind them for a moment; the myth that targeted ads systems actually work as intended anyway is complete bollocks. As far as I can see, targeted ads only seem to be able to tell me what I have bought in the past, or are completely irrelevant. I think I've yet to see an ad that has been related to something that I have been actually browsing for, or has had the prescience to know what I want whilst I am browsing for it. Amazon seem particularly shit at this.
I remember being on a scuba diving site once looking to book a holiday, and seeing ads being presented for kitchen white goods.
Shit. Just shit.