The functions:
http://mongodb.github.com/node-mongodb-native/api-generated/collection.html#count
and
http://mongodb.github.com/node-mongodb-native/api-generated/collection.html#insert
do not document the arguments to the callback function. For insert the examples don't use the second argument so it's not clear what it is for.

An example where the arguments are documented:
http://mongodb.github.com/node-mongodb-native/api-generated/cursor.html#count