Meaningful research experience is always a plus - doesn't matter what field particularly - but "meaningful" is the key. I encourage med students to get involved in research because it can be a great learning experience, a very different one from the classroom or the wards. It can help you become a better thinker and a better physician, and might even open up some new career interests. Plus, meaningful research really strengthens your CV.
There are several ways of showing that you did meaningful research - a first-author publication is clearly helpful in that regard. Other things to keep in mind, even if you aren't lucky enough to get a first-author publication:
1. It's important to spend enough time on the project that you can learn something in-depth - after all, it should be first and foremost a learning experience for you - and enough time to see the fruits of your labor - i.e. achieve meaningful results. This is very difficult to do in a summer. Ideally, invest a minimum of one year.
2. Produce a finished product of some sort - i.e. present your work in a major forum. You will get more out of it if you see the project through to an endpoint, not to mention it gives you something tangible and credible to put on a CV. A publication is great.
3. Get an outstanding letter of rec out of it. Research is a great way to get to know faculty outside the traditional attending-med student relationship, which can add a unique dimension to your letters. Plus, if you follow #1, your research mentor will know you better than probably any of your clinical attendings, so the letter will be more insightful and more meaningful.
4. Related to the above, it's helpful, though by no means necessary, to do your research with someone influential, i.e. the chairman of the dept in the specialty you are considering. This can be very helpful if you are considering an ultra-competetive specialty, but again is not necessary.
