If you try building a realtime single page app using Meteor and measure the amount of time it took you to complete it, you'll find that the hype is justified.
But at the expense of performance? I've written a number of applications in Meteor and continually struggle to scale them, even to tens of concurrent users.
Well http://mostexclusivewebsite.com/ currently has 46,000 users concurrently connected, in-line, receiving live updates, waiting for a ticket. So yeah, I would go so far as to say that Meteor can be scaled pretty well.
I've just tried to access the site and it's failing to load half the time, and the other half it's taking over a minute to load. It's awesome you're getting traffic but I'm not sure you can say you've successfully scaled your app right at the moment.