Link: http://www.schneier.com/blog/archives/2009/05/an_expectation.html

Quote:
If your data is online, it is not private. Oh, maybe it seems private. Certainly, only you have access to your e-mail. Well, you and your ISP. And the sender's ISP. And any backbone provider who happens to route that mail from the sender to you

You could encrypt your mail, of course, but few of us do that. Most of us now use webmail.

Full story here

Also check "Privacy vs Nothing to hide"