Ok, this is a really awesome hack that scares me... You go to a website in a tab, then you click on one of your other tabs or walk away from the computer. The website in the first tab realizes that you aren't looking at it anymore, and changes its title and appearance to match a website you've recently used (it can find this out by looking in some of the data your browser saves to make loading the page faster the next time you look at it). You put in your log in info with out looking closely at the url, and they just stole your log in information.

This website demos it (it works in Internet Explorer and FireFox, but didn't work in Chrome - which doesn't mean that Chrome is any safer):
http://www.azarask.in/blog/post/a-new-type-of-phishing-attack