If you are posting personal information on an open webpage, expect harrassment, sooner or later. Blogs and MySpace accounts are not immune. Online dating services have taken some measures to protect information, but the bottom line is unless the site is some type of completely private, user authenticated affair where only the people you invite in (i.e. people you already know) get to see your headshot, then you are playing with fire.
Jason Fortuny’s “experiment” (results posted at Encyclopedia Dramatica) with Craigslist personals highlights this lack of privacy. While Jason is bragging away about the publicity he garnered I am sure there are quite a few men hunting for his name, address and phone number.
This doesn’t stop at webpages either. Any email you send may very well get circulated to others – while you have some minimal protection in the fact that forwarded email generally doesn’t contain previous header information (instead just a copy of the original text), what you say and what you attach are fair game. If it is confidential/company information, don’t send it period. If it is nude photos of yourself on a lawn chair, designed to lure some overnight company while the spouse is away, have at it – you are likely already doomed.
Wired has an analysis of the “experiment” – they are calling Jason sociopathic. I’d tend to agree, although I’ve seen email sent to people considered credible, “pillars of the community,” find their way back to the sender with very “colorful” commentary.