We've built a huge meteor app that has scaled to 1000s of concurrent users and still growing -- there have been some sticky points along the way, but overall, we're extremely pleased. Meteor is an amazing engineering feat.
We will be sharing more soon. We've been developing with Meteor since the winter of 2012 and two main scaling issues have crept up: (1) the web tier was a bottleneck prior to 0.7.0's implementation of oplog tailing; and (2) post oplog tailing, mongo actually became our bottleneck with the write locks. We were able to get to about 3300 concurrent users (in our very data-intensive application) against a single beefy mongo primary before the database started choking, and at that point, we could set our readPreference to the secondary in order to further scale horizontally.
"We" are providing a large scale application in the education space, with more details to follow. I am not able to give much more now, but I can say that given the contractual nature of our application, we've been fortunate to start out with a HUGE user base that has taxed Meteor and exposed its scalability issues more than most typical Meteor apps at this time. It's still young, and there are some significant advances that can be made to its oplog driver, but overall Meteor is incredibly forward-thinking compared to other full-stack implementations. Philosophically speaking, you must be all-in, however, otherwise you will always kick against the goads. As everyone's favorite theologian would say.
"Apparently, "to kick against the goads" was a common expression found in both Greek and Latin literature—a rural image, which rose from the practice of farmers goading their oxen in the fields. Though unfamiliar to us, everyone in that day understood its meaning.
Goads were typically made from slender pieces of timber, blunt on one end and pointed on the other. Farmers used the pointed end to urge a stubborn ox into motion. Occasionally, the beast would kick at the goad. The more the ox kicked, the more likely the goad would stab into the flesh of its leg, causing greater pain."
