When someone who has been following you, decides not to, wouldn't it be nice if they were offered the opportunity to state the reason why they stopped following? (Of course, providing this feedback would be completely optional.)
It seems to me that quite a lot could be learned if people who stop following are given the opportunity to say why -- if they use this opportunity (I know I always would like to know the reason(s)).
AND: I suppose it might also be very useful if a similar opportunity, to provide feedback (optionally), was also presented to a person when she/he STARTS FOLLOWING you -- who knows, one might learn who has interests much in-common or very much congruent with your views or approaches.