Even without hacking, what people can do is astonishing.
If they've got a mate anywhere in admin team, they can get your email and probably plenty more. I can't help but notice I once asked a glazing company for a quote about doing my windows, and within three months I got about 5 other glazing companies soliciting me: I believe someone gave the first firm's customer database to rivals - and it only needs one corrupt employee at a firm to hand out an awful lot of data on a person. In many chat rooms, your IP address may be exposed: I was slightly alarmed when I went into one for discussions on an online game and someone told me what city I was in from my IP. One chatroom I was in years ago you had to register with your email, and for someone who knew the system your email was part-visible publicly.
Casually chat on a forum like this long enough, most people probably incidentally leave enough information about themselves - place of residence, hobbies, job etc. - that a determined investigator prepared to trawl through might be able to identify them, or at least narrow the possibilities down a lot. Plus of course probably the user also revealing what other sites they use, for even more info.