I have heard tales of folks having told cardiology fellowships they were #1 and then not ranking them #1, and the PD told me that later the person applied for a faculty job @the place and was rejected. However, I think it's rare for this type of stuff to happen. I wouldn't go tell 10 placed they are your #1, but if you told a place they are #1 and then later changed your mind to a different place, I don't think they are likely to remember you 2-3 years down the road and be mad. Also, PD's have learned not to believe what applicants say, just as applicants have learned not to believe what programs say.