The latest 1.1.0 release includes the ability for the driver to read from slaves. By default it will randomly pick any of the members in a replica set.
There are some instances where we would want to exclude certain members e.g. if the member is used for disaster recovery only and is in a different data centre or if the member has a syncdelay.
Therefore it would be useful to be able to specify members to exclude. By default it would include all, but with the option to provide a blacklist (rather than a whitelist since that would require changes every time we added a server).