Lewis Black put it best:
We don't have a culture. We have cable.
That is to say, Americans don't just have one homogenous culture; rather, we have 80-plus homogenous cultures into which we fit with varying degrees of accuracy. America has no official language1; while most people speak English, a rapidly increasing number of "minorities" speak Spanish, Chinese, Korean, or any number of other languages. Similarly, if you visit a city or town with a large number of non-English speakers, you will notice a culture vastly different from the norm you see on television.
A lot of people are able to keep aspects of their homeland, creating a comfort zone in an unfamiliar country. The Religious Right and white-supremacist groups insist that this is depriving America of its roots. However, the influx of different cultures has reshaped America. In many towns now, you can actually get more "authentic" East Asian cuisine than ever before. There are multiple Spanish broadcast networks: Galavision, Univision, and Telemundo, to name a few. Churches offer worship in multiple languages, with Korean churches seeing a particularly fast growth rate. The second-generation folks -- children of immigrant parents -- tend to join the mainstream while subconsciously injecting their own culture into their circle of friends.
Americans are free to behave as they please in this regard. Some feel comfortable with a group that speaks their own language, while others are more drawn towards the commercial mainstream. It is this spectrum of choices that makes America truly unique.
1 Source: http://ask.yahoo.com/ask/20011107.html