I have one W from over one decade ago when I was taking summer classes at home in between years at college. I literally missed the drop/add deadline by one day for one of the classes, so I got a W instead of nothing on my transcript. I withdrew from the class because the description didn't say it was a hybrid online/instructional class and I did not want to take a science class online.
Anyway, no one said a thing. It was was a non-issue in the admissions process. I think it would be an issue if you had an alarmingly high amount of Ws throughout your schooling; if you have a bunch of Ws for one semester due to a personal or family issue, then you have a chance to explain what happened.