So unless you win the Google lottery you have a choice between having AT&T watching your every packet or Comcast's Standard "Oil" Cable monopoly in progress. No Google for me so it's essentially a Hobson's choice for me.
Sure, now they're all about unicorns and rainbows, and talking the good game to get into what is a very capital heavy market. I can easily see Google switching to this exact same model to inject Adwords and extract even more money from subscribers once they're hooked. The difference is Google won't let you opt out.
It's the difference between tracking only by server/client tricks (IP, cookies, hit logs etc.) vs. tracking by the ISP. The former can be avoided by client config, the latter only with a VPN.
Even if they let you supposedly opt out of the DPI, who trusts a corporation like this? And as adestefan notes, where do people get the assumption that Google is not doing the same?
Edit: I finally found ATT's (semi-) disclosure about this: http://www.att.com/esupport/article.jsp?sid=KB421828&cv=812
It says that if you don't opt out they collect " webpages you visit, the time you spend on each, the links or ads you see and follow, and the search terms you enter" - but there is no statement that they're not collecting that info if you opt out. All they promise for opting out is not targeting ads with that data.
Google dominance in the ISP market will probably have its own share of problems for consumers, but I hazard that they will be different and less infuriating problems than what we get with the current status quo.