[OliC]

Replacing the title with "Come back! We miss you!" when you leave the tab is cute but it makes finding the article in a sea of tabs difficult.

[grundprinzip]

It's an awesome eye-catcher, they should make a JQuery plugin (if it doesn't already exist). And the code is rather (minified) simple:

https://gist.github.com/grundprinzip/5868304

[Killswitch]

No need for a jQuery plugin, it's simple to do. I noticed it too and looked through their JS and found it to be way more complicated than it needs, using jQuery.

http://jsfiddle.net/Killswitch/BSukL/show/

Nothing on the page but the code, so open that in a new tab and swap tabs to see it in action.

[bluetidepro]

I completely agree. It's awesome in theory, but I would hate this feature if tons of sites started using it. It could get out of hand very quickly.

[recursive]

I don't know what theory it's awesome under, but I have to disagree with that. I want titles to describe the content of their page.

[brokentone]

I didn't find it cute, but rather annoying.