Honestly I learned about the PHP mongo extension by going to MongoDB's website & reading how to get it to work. My first thought was not to do 'pecl install mongo'. This probably has more to do with 10gen taking the effort to write a proper extension for PHP rather than letting the community come up with a module for node.js. Also I don't think node has had time to "settle" since it's still evolving, so you'll experience package fragmentation like what you see with mongo.

I do agree that along with package management there should be a strong community/social component involved that critiques & communicates about packages available.

npm's tracking of dependencies, and potentially downloads, could be used to help tier packages in search. You can currently see the most depended on packages, as well as the packages that depend on individual packages, but this could be taken further to help establish PageRank like authority.