Be sure to use Node's cluster API (http://nodejs.org/docs/v0.6.0/api/cluster.html) so each core on your server gets utilized. Doesn't look like this, looking at the source, is doing that so unless they're manually running an app instance on each core and load balancing between them then they may be underutilizing their hardware.

Beyond that: using Nginx to serve any static assets (http://stackoverflow.com/questions/5009324/node-js-nginx-and...) and standard stuff like making sure everything's cached that should be, load balancing, etc.