Since I heard about Famo.us I was always excited about the possibilities it could bring to web application development.
I feel like we were teased with demos from the Famo.us JS team of Facebook Paper/Flickr clones that looked gorgeous, and of which source/sample code never materialised.
What the Famo.us JS team were doing looked fantastic, and without understanding all of the technical aspects behind it, I wanted to use it. Uptake was low and generally the bleeding edge community steered clear from it. I guess the writing was on the wall as a result.