Playing with it. It's interesting if you want to build both client and server, and care somewhat less about SEO which isn't all that easy. Also it only supports Mongo at the moment with Redis in beta. Jetbrains new Webstorm 9 supports it (mostly) out of the box.

For the SEO piece there is the Spiderable package. It uses phantom.js to build the page and send it back to crawlers.

"[Building meteor] was hard. 'This is a challenge up there with building Unix or Windows'"

To be fair, the actual quote refers not to Meteor development, but to the realtime platform built for Asana in 2009:

"People just wouldn’t wait around for the application to sync each change with the server. So before they even began coding the actual task management features, Schmidt and company spent months building their underlying framework. It was hard. “This is a challenge up there with building Unix or Windows,” Schmidt says."

Good thing he built Unix and Windows, allowing him to make this informed comparison.

The open source platform in question is Meteor.