Seems like they should be ranked by SLOC or number of total watchers for their packages.
Heck, someone could go and published a lot of useless packages and get on the list! (if that kind of vanity was your thing)
edit: michael jackson codes Node.js @ #310
Other good metrics would be issues and pull request activity. A product with lots of pull requests and solved issues is one that is actively being used by people that probably matter.
It would also be good to be able to rank modules by tags so that questions like, "what are the highest ranked testing libraries?" could be answered.