I don't understand why conservatives and "libertarians" have such a ridiculous kneejerk reaction to the phrase "common good". America has always had an eye toward that philosophy.
There is no denying that as Americans, and more importantly humans, there are some goals that we all agree on and share, therefore, as a society or the largest of special interest groups, we can use the tool that represents us all to accomplish these shared goals. If we all agree that there is an agreement that a certain goal that we all share, the use of government to accomplish these goals is the best way to reach that goal.
Examples of "common good" ideas that have been addressed by the government, for the most part, effectively. Clean water, for instance, is a notion that we all share and desire. The government can set rules to ensure that the populace can safely drink clean water with ease. The nations highways, I believe are a result of "common good" thinking. It was good for business, for vacationers, good for all.
"Common good" thinking can be exemplified by the our laws against murder and theft.
"Common good" thinking is responsible for the idea of public education. Simply put, a more educated populace is a freer, more productive populace.
The military is the ultimate in "common good" thinking. Protection works for everyone. Attack works for a few and that's because it steps away from "common good" thinking and serves a special interest. Those who support the war are in actuality trying to make people think that attacking Iraq pre-emptively was for the "common good". (Though that has been proven a misconception over and over.)
Firefighters are a result of "common good" thinking. Police forces, as well.
So, when you're whining about the Dems "new" slogan, remember America was founded on the idea of "common good".