"The internet is not secure, and neither is your data."
"It is the norm to assume that no thought needs to be given to how our trust is managed."
"Our current method of securing transactions over the internet was designed before there was a need for it, and the concept of "authorities" was only added as an afterthought."
Whichever of the previous statements makes you the most nervous about online banking, online shopping, email, social networking, or anything else you do online, choose that one as the opening statement for this article. As usual, I will be brief, but I encourage you to watch the video that I link to. It's from a conference, and is voice and slideshow. Some people will certainly find it dry, but try to keep in mind that the companies and people mentioned in the presentation are the same ones that you are allowing to manage your trust on the internet. You might not care about "how" it's done, but you should certainly know if it stops working completely; I'm sure you would have reservations about sending personal information through the mail if you discovered that it was possible for anyone, anywhere to read everything that you send and receive, without either party knowing.
Here's basically how it works. When you log in to a "secure" site, you will see in the address bar of your web browser that http changes to https, and in many browsers the background and/or foreground colour will change. When you are using https, you will also have the option of clicking on "https" and viewing information about the certificate.