Akuperman is right that the lines are much less clear in the US, and outside of the New York/New Jersey areas they are even less clear. In Israel, one really has to choose whether he is Chareidi or Dati-Leumi. These are very definite labels and they determine everything including what schools you send your kids to, who your Rabbanim are, and what your kids end up doing after high school.
In the United States, there are not such clear-cut labels, and it is possible to get away with having no label at all.
I agree with you Penp that it is very important to know the differences between America and Israel for shidduchim. I have dated in both Israel and the US. When I am in Israel, I am not likely to date a guy who is not Chareidi, but in the US, I am much more open to dating guys with different labels.
In the US, I don’t have to define the guy by his label, because in the United States, someone who is not Chareidi can still have a chareidi Rav and send his kids to the same schools that I would. Also, the Zionist issues (like whether or not we should send our sons to the army) are not really issues there. The only Zionist issue in the US is whether or not he says Hallel on Yom HaAtzmaut, and who cares?
Another difference between the US and Israel is that in the US people don’t usually use the terms Chareidi and Dati Leumi. The equivalent terms are Yeshivish and Modern Orthodox, but they don’t mean exactly the same things as Chareidi and Dati Leumi. It is also confusing because the term ‘Yeshivish’ is used in different ways by different people/communities.
If someone has Chareidi hashkafos but doesn’t dress Yeshivish or watches movies or goes to college/work, he would not be considered Yeshivish by most people in the American Chareidi world, but most Modern Orthodox people would call him Yeshivish.
The term Modern Orthodox is also confusing since it has a wide range of meanings. It can refer to someone who doesn’t keep all the halachos (for example, hilchos tznius), or it can refer to someone who is makpid on halacha but does not have Chareidi hashkafos (generally in terms of issues such as Zionism, Feminism, secular studies and listening to Daas Torah). Sometimes, the term Modern Orthodox is used by people simply because they do not feel comfortable in the Yeshivish world for sociological reasons, since it’s not the type of community they grew up in.
Hope that helps. You can ask me to clarify if you want. I have lived and worked and dated in different types of communities in both countries so it is a topic that I am fairly well-versed in.