Many here are making what I believe to be an important distinction between two very different groups within MO. There are MO who live up to MO ideals, and embody the concept of Torah u’Maddah, whether you hate it or love it. Then there the self-identifying MO who would probably be more accurately classified as Orthodox-lite: those would like to get away with as much as they can while (in their own minds) staying just within the confides of authentic Judaism. The differences between these groups is most obvious when one compares their fealty to Halacha; the first group will usually keep it scrupulously (although not most of the stringencies that those on the right keep), while the second will often times just ignore it.
The difference between the “ideal MO” and the average “baalabos” are indeed not too great. For the most part I agree with the differences listed by DaMoshe (if not the slant that he put on them):
Chareidim tend to believe that it is best to try to remain as unaffected as possible by the permissive culture that surrounds us. MO tend to believe that there is nothing wrong with immersion in that said culture (or that the benefits outweigh the risks). This difference manifests itself in watching TV/movies, listening to non-Jewish music, reading non-Jewish books, and limiting internet access.
Secondly, as indicated in the YU slogan Torah u’Madda, MO tend to believe that any knowledge is inherently important and worth pursuing. Chareidim tend to view secular knowledge as nothing more than a means to an ends.
Then there’s Zionism, which is technically a separate discussion (it is possible to be Zionist and Chareidi, as well as anti-Zionist and Modern) but one who’s fault line on these shores are often drawn between the Chareidim and the MO.
However, there is another distinction as well (besides attitudes towards chumros, which I mentioned above): The question of balancing one’s obligation to support one’s family and one’s obligation to learn Torah. Chareidim will usually try to stay in learning for as long as possible, even if that means supported by their parents/parents-in-laws, wife, or government programs. MO tend to focus on earning a livelihood starting from shortly after high school.
If one is looking for extensive review of the ideals and current state of MO, I would advise reading R’ Aharon Lichtenstein Ztz”l’s essay “Centrist Orthodoxy: A Spiritual Accounting”