Just found a great article by Jeff Harrell on how Node.js is being used and implemented at PayPal.
“Like many others, we slipped node.js in the door as a prototyping platform. Also like many others, it proved extremely proficient and we decided to give it a go on production.”
Some companies might start with a small test application, or something non-mission-critical. Not PayPal. They went big, deciding to use node.js to implement their account overview page, one of the most heavily trafficked apps on the site.