If you add a comment to my blog then I get to know your e-mail address and your IP address. WordPress.com does not make this fact obvious, that’s why I mention it here.
I regard this information as private. I will not deliberately share it with anyone except when I believe myself to be legally obliged to (for example, a court orders me to do so). If I share private information about you with anyone then I will tell you so if I am legally able to do so. If you ask me with whom I have shared your private information then I will answer if and only if I am legally able to do so.
However, if you’re trying to hide your identity in order to be an asshole then I’ll probably break these rules.
WordPress.com may well have their own ideas about what to do with your private information. So far, they seem like an okay bunch of guys.