Also it depends on the circumstances which led you to withdrawing. Obviously we have things like "excused withdraws" but you might not always have enough paperwork to warrant those. So I guess it just depends where you are getting these w's. If you are getting them in specific classes, like maths, that might not look to well since they can assume that you obviously are having specific problems with those classes. Similar goes for sciences. In general, they have to be spread out among different type of classes. You can not just continuously be withdrawing from classes that are specific to your major, as that might raise suspicion that you are simply in a major that you should not be in.
So preferably there has to be some sort of trend in the withdrawals. And even better if they happen within a semester or two together as that might support something like "having personal issues" that caused you to withdraw. However, it is not good if it just all over the place, like if you are withdrawing from specific classes but are passing "easier" classes with flying colors, that might not look to well.
Basically, people withdraw from classes for varied amount of reasons. Just as long as it does not look like you are withdrawing simply because the class is hard, you should usually be fine with having a number of w's.
Even after all that, the most important thing is to have some sort of an upward trend after the w's, anything that will show that the w's were just a one time thing, and that in reality you are capable of doing so much better.