Seth Godin (marketing expert and one of my Facebook friends) wrote this in his blog today. I have reproduced his blog post verbatim as they are very very wise words:
If you think that's a friend of yours on twitter, don't be so sure.
If you wonder why your boss sent such an insane email to you, don't be so sure.
If you get a chance to invest online, think twice.
Don't buy anything from an inbound phone call.
That email you sent in confidence... probably won't be read that way. And that photo, yes, it's going to show up in the digital world where you least want to see it...
In your little village, where you see your neighbor every day for ten years and the person in the next car might be the local constable, the rules are very simple and obeyed by all. In an electronic world, it's trivial to impersonate, hack and otherwise annoy.
Online, rely on direct, personal interactions to be sure you're seeing what you think you're seeing. Trust, but verify.