To explain a bit so you 'get' what she was referring to. Two problems present themselves with a public site such as PM. First, you have to login to the site from somewhere "out there." From a public PC or even your own, the password and/or cookie value might get 'sniffed' on the wire. Second, as Petruchio so visibly reminds, this is a public site and while clicking around your cookie value might get sniffed.

So it is not your email account that is worried about in DigitalKittys question. It is your PM identity, which could be cracked, co-opted, the email address changed and then how do you get it back to being accessible only by you? So, back to the original question...