I would say that sometimes you do and sometimes you don' t. I think it depends upon two factors: the deer and wind direction. I have sat in the open sometimes with camo and sometimes not, if the wind is right and you are still SOME deer will look at you and go about their business. Other deer will run at the sight of you even when in camo. Now if the wind is blowing in the wrong direction then any deer (except maybe one that' s retarded) will take off instantly if they smell you.
Yesterday I had a button-buck feed and browse all around me for a half an hour. He stopped to watch me many times. Then, at maybe twenty feet away he decided to lie down for a nap. I thought about taking him as a doe then changed my mind. After a while I had to adjust my position and in doing so I rustled some leaves. He got up and casually walked away. I guess he felt something just wasn' t right.