I wouldn't go so far as to say everyone knows that part of their Facebook profile is viewable to the world, but one should still assume that any information pos

I wouldn't go so far as to say everyone knows that part of their Facebook profile is viewable to the world, but one should still assume that any information posted online is public, even if said person has some quaint notion of privacy. Simple rule: if you don't want it made public, don't put it on the internet. As for ethics, I don't find anything wrong with using information gained using this method unethical if it's used in an aggregate. If, as the article suggests, you use it to find out that the majority of your users are gay, you might be able to fine tune your site to better serve their needs. Or it could reveal to you that your site is too niche and make you generalize it better. If you use it to cold contact random people using their personal information gained surreptitiously, then your ethics could certainly be questioned.