If you think you want to do one of the really competitive specialties like Derm, Plastics, Neurosurg, etc. then research/publication is essential and the summer before starting is an excellent time to get started on this (IMHO). I was just discussing this today with other 1st years about how if you talk to physicians in these specialties they tell you it's mandatory to match well while the administration and a lot of others tell you to relax and enjoy your last (or second to last) summer off. I did some research the summer before because I was already involved and enjoyed it. That was time off for me. I didn't publish but called on my PI later for help me with a LOR for a scholarship application and to get into another lab the summer following MS1. So, bottom line, if you are shooting for a competitive specialty or just enjoy research, by all means do it. Even if it doesn't get you published, it will likely help you indirectly in other ways.
On the other hand, while this might put you ahead in a small part of the game, if you choose not to it will by no means put you behind. Also, all the research in the world isn't gonna do much good if you're burnt out your first two years, don't learn the material, and score poorly on your boards. So, as with all things, balance these choices with your life and sanity.