Granted that I won't be applying for residency until the summer (and not in derm) but having done a moderate amount of research in school, here is my opinion-
Everyone who does research obviously wants to publish and doing so is a huge accomplishment. Having that gem on your CV will definitely draw the adcom's attention and might bump you up on their list of candidates.
But even without a publication a great research experience is certainly not useless. There is more to be gained from research than just data tables and figures. Anyone can join a lab for a few months, pipette a few things into some other things, run a gel, get their name on a manuscript, and submit it to a crappy journal. But if they were only another "set of hands" in the lab they probably didn't grow much as a scientist or critical thinker, and this will show when asked about their project.
Then again you might be in a world-class lab and be doing world-class research with a great PI. And yet, because of the nature of research, your experiments simply don't work out or your results completely dispute your *exciting* hypothesis and no one wants to publish it. I would not call that a waste. You set out to ask and answer a scientific question and you did it!
I won't hesitate to put any of my research experiences on my CV regardless of having zero pubs because they've all taught me a great deal. If that keeps me out of a competitive program over someone else because they published a study with a N=2 in a throw-away journal, well you know what they can do with their program spot.