Where anything network related is concerned, has anybody heard anything about the ICO's investigation into the use of systems by Shine in 3UK's network? It seems to be something that both the ICO and 3UK would rather pretend never happened.
And that's the problem that could prove to be a big stumbling block for network level blocking: getting consent. Something that 3UK or Shine still have to explain how they intend to achieve, despite jumping the gun and announcing the trials back in February.
In order to identify the adverts you have to be able to examine the content of the page. That means - for network level blocking at any rate - giving the network the ability to see every page that you've requested (although how they'd do this with SSL protected pages without resorting to some sort of man-in-the-middle style attack remains a bit of a mystery).