Major - P3 Description
The Upgrade Guide in the library documentation would do well to note changes to BSON classes between ext-mongo and ext-mongodb.
This came up via doctrine/mongodb-odm#2038. Since Doctrine ODM 2.0 will be changing its dependency to ext-mongodb, this information could be useful to ODM users that will be migrating their code from the old extension (or new extension, with adapter library).