Quoting from his website "Yehuda Katz is a member of the Ruby on Rails core team, and lead developer of the Merb project. He is a member of the jQuery Core Team

Quoting from his website "Yehuda Katz is a member of the Ruby on Rails core team, and lead developer of the Merb project. He is a member of the jQuery Core Team, and a core contributor to DataMapper. He contributes to many open source projects, like Rubinius and Johnson, and works on some he created himself, like Thor." But what that doesn't say is his contributions through his blog (both personal and EngineYard blog). I have learned more Rails 3 from his articles than anywhere else. He co-authored a book called 'jQuery in Action'. Another excellent read. To answer your question directly, Yehuda adds a lot of value to whatever he takes up. Apart from writing excellent code he explains it succinctly through his writing. SproutCore will benefit from this.