Of the two public people who left Engine Yard, Ezra and Yehuda, they have different qualities. Both notable and oft overlooked in our tech-bent community.

Ezra writes technology and Yehuda informs technology.

I see Ezra doing things beyond me. I see Yehuda bridging the gap between myself and Ezra.

It doesn't matter where they are. Watch each with their strengths and you will see fantastic things.

The output of this guy is amazing, any OSS projects he works on will move forward and benefit a lot of people.

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.