Difficult to know where to put this, there should be a security section in all forums afaiac, but there isn't so here goes.
I got what looked like a phishing email from paypal the other day, you know the sort of thing - Your account has been suspended. please log in and reset your password. Logged in and the first thing it did was to ask for my credit card number. Hmm? The site looked genuine even down to the security certificate, but even these have been spoofed in the past so I wasn't happy and forwarded the email to their security department. It turns out it was in fact a genuine one. Whilst looking into it, I also had a read through Paypal's security section and noticed something which I hadn't heard of before and which, for the want of a few clicks looks like it's worth while turning on if you are a Gmail user. It is called "Authorisation icon for verified Senders" it's a Labs feature, so if you want to use it this is the procedure.
Log in to your gmail account, click the 'gear' icon near the top right, select settings and then choose the 'Labs' tab. Look down the list for the feature and click to enable it. I know it works because as soon as I enabled it, the message from Paypal had a key icon displayed alongside it in my Inbox indicating that is was genuine. Pretty useful in this case, though I don't know what mechanism it uses to authenticate, they don't tell you that.
At the moment it only works with Paypal and ebay, but hopefully it will extend its 'reach' in the future. I would guess though that most people on the forum would have an account with one or the other of those two if not both, so it is a feature worth using even as it exists now.