At my school it's a required third year rotation, and there are opportunities to get involved with the emergency med folks as a preclinical student as well. I have to admit, I didn't care for it much -- lots of primary care (which because of the lack of continuity, I never felt like we were doing good primary care), no follow up. People who like it tend to cite the relatively undifferentiated patient at presentation, fast pace, procedures, variety.
If you know you're interested in EM, you might want to contact the faculty and find out whether they have any research or shadowing opportunities (usually they do). It'll get you in touch with people in the field and may help your application down the line.
Anka