Not just concerned
"Both the US FTC and the European Union are currently concerned about Online Behavioural Advertising (OBA) in particular, and the tracking of individuals across the internet in general..."
The EU is more than concerned having issued a directive effectively banning all cookies without *explicit* prior consent in 2009 with a requirement for member states to enact legislation by May 2011. Of course, as is their wont few governments have actually passed legislation but they will be required to do so and then the lawsuits will come.
Limiting cookies to the current session is probably the minimum restriction that anyone can get away with but with more and more applications being "always" on that probably isn't enough and third-parties are probably doomed and trackers will only have themselves to blame.
In fact, if you look at what HTML5 offers then cookies themselves are probably on the way out - local storage and websockets are a good replacement and a browser-enforced solution is probably the only practical approach. "You need an HTML5-capable browser to use this website" notices could provide the necessary kick up the arse for the laggards. Except those millions stuck with IE 6 for reasons of compatibility...