In a recent Meteor video, Hansoft were discussing how they encountered (and solved) O(n^2) issues in meteor core that limited them to 100 users before things erupted into flames. I wish they had spent the entire talk on that topic alone.
Being new to meteor it’s a frightening thought that these issue not only exist, but are an unknown as they are rarely discussed. Somewhat difficult to make application design decisions, let alone infrastructure ones.