The necessity of research experience is highly dependent on what type of schools you want to attend, as Concordia alluded to. If you are thinking you would like to attend one of the top 20 schools, research becomes rather useful in your application. Those schools are ranked where they are because they bring in a lot of research money, and thus perform a great deal of research. That's not to say that you cannot get into one of those schools without research experience, it just makes it a little more challenging, and you will need other strong activities in your application.
Regardless of whether or not it is important for the particular school you hope to apply to, I would recommend attempting to get involved with some research if at all possible. You may find that you really enjoy it, and it may influence what type of medicine you want to practice (academic vs private, for instance). Best of luck.