I agree with Mounte.....
Don't feel you need to do this to get a step ahead of your fellow students. It is not necessary! If you want to just "get a feel" for the ED before your third year starts or you just have an afternoon to blow, go ahead... but don't think it will make a significant impact on "landing you a residency position." You will be spending more than enough time in the ED or the hospital of your choice during your third and fouth year... AND its important to know that as an observer, they aren't really even critiquing you or evaluating you as a potential applicant/resident... you are still a neonate in the eyes of the attendings and residents...
BUT..... if you just want to hang out just to pass the time or to just experience some of what goes on in the ED, it won't hurt. Just don't do it thinking it will land you your #1 choice.
Q, DO