People dress up, drink, and party. At my office, the company is sponsoring a big party at a disco for all the employees with alchohol and kosher food. Unfortunately, most of the people have no idea what Purim means. In America, the average non-religious Jew never heard about Purim, let alone celebrates it.
I don't know if this is a good thing or not. On one hand it is good that at least people have some awareness of the Jewish calender and that there is such a holiday as Purim. On the other hand they have completely forgot about what Purim stands for and what it means.
In one respect it is good, it gives the religious and non-religious a common language. They can talk about celebrating Purim (even though the celebrations are radically different) what the kids are going to do dress up as etc.