For a couple of Ws, I don't think it matters much, but 7 is quite a few.
It's going to depend on:
1. The pattern of Ws. For instance, if you have several one semester because you were ill or had family emergencies, that's pretty easy to explain. However, if you had 1-2 every semester, that might raise a red flag that you pull out late when your grades are sub-par. Most schools have pretty liberal drop dates so if you don't like the class or prof you can drop it early without a W on your record, so consistent late Ws are not that easily explained.
2. The rigor of your course schedule after you withdrew will also be important. Dropping consistently from 16/15 to 13/12 units per semester is going to look a lot different than going from 20/18 to 16/15. And the level and type of courses will matter too.
Last edited by entomom; 11-09-2012 at 06:58 PM.