I thought it was bad, but it isn't. After 4 years of undergrad, I just got my first W this semester. I asked my major advisor and my professor who's class I got my W in. Both of them said it's ok. They said things happen (i.e. family problems or you didn't like how the teacher was or how s/he lectured, etc.) I thought it would ruin my chances, but it didn't. We live and learn. My friend got over 20 W's and got into UCLA for med school. So yeah...if you're still good with everything overall, one R won't hurt you.