I know of two people from my school who did this, both of whom matched very well. The reasons for doing this range from undecided on specialty to waiting for significant other to wanting a break to building your resume. You can do research in pretty much any specialty you want, but since you are not in medical school, I do not believe that the medical student research awards would apply to you (Doris Duke, NIH cluster, etc.). So, you would have to find a lab with deep enough pockets to fund you for the year. If you didn't want to do research in this year, that would be more of an issue in applying for a subsequent residency.