Blocking Google's targeted advertising

Google have announced they will be launching behaviourally targeted advertising (The Guardian: Google introduces targeted display ads on sites including YouTube).  However, as a poster on the nodpi forum points out, there are significant differences between the Google strategy and that of Phorm:

Phorm uses intercepted ISP traffic - Google collects its OWN data and is easy to block.
Google is just a website - Phorm infiltrates an entire ISP network

Rather pleasingly, and this is in stark contrast to Phorm, Google provide instructions for permanently opting out of the system.  The instructions for Firefox can be found at Advertising Cookie Opt-out Plugin, where there are links for the instructions for other browsers.