I don't understand why this keeps going on....
This is not an issue for webmasters at this time, if anything its good if you want to look at it from another perspective. Ads from Phorm will be shown on your site only if you are participating in the program. The ISP collects the data from the user, if you are participant in Phorm's ad program you can show ads on your site. Instead of being based on the content of your site the user can get served with ads based on their browsing habit.
As for the user its a huge privacy concern.
There was only two things that were brought up by someone else with this system IMO that should make a webmaster concerned. Your content is being used by the ISP to produce a profile for the people that visit your site and you're not being compensated for it. The other and more important issue IMO was they could analyze content that was behind logins not available to the public.
There is only one instance that I'm aware of that was absolutely confirmed where ads were injected by an ISP into content that was confirmed. This happened in Texas when an ISP "accidentally" turned it on for a few days. They were using the Nebuad system which is about the same thing as Phorm. There was another thread on here where it was suspected that they did it for very short time with Phorm but I don't know if that was absolutely confirmed.
IF they start injecting ads then there's an issue as far as I'm concerned. I've said it before, I'll block any and all ISP's that inject ads. I don't care if I have to go down with the ship doing it either. No hacks, no messing around. Simple redirect to a page with a big giant arrow pointing to the ad stating this ad is served by your ISP therefore you cannot view this page.