From Digital Inspiration:
The number 404, the error message displayed when a browser cannot find a webpage, is now a part of the vocabulary of non-geeks as well, who commonly use this word to mean that you or the person you are referring to is clueless.

Delicious
Digg
Ember
Facebook
Feedburner
Flickr
Foursquare
Friendfeed
Google Buzz
Gowalla
Last FM
LinkedIn
Posterous
Qik
Slideshare
Stumble Upon
Tumblr
Twitter
Vimeo
YouTube





