On the people around me. Roommates, coworkers, romantic interests etc. Obviously none of them know this and I'm not here to ask for advice on whether or not it's a good idea, psycopathic or morally black or white. I just want to know what are some things that I should keep in mind while doing so. If I ever have to use the information I've gained, then it has to be as complete and trustworthy as possible.

Edit- so far I've been told that it's either a good idea, bad idea, questioned why I would do it, and reminded to keep things secure. Now while I appreciate the collective concern, no-one has yet toanswer my question, even though I specifically said I don't need other info. Because of this, I'll post the question again in bold: what are some of the things that I should be on the look out for while I do this?