MongoDB Server 2.0 supports a number of new features with getLastError which the driver must support:

• the boolean field "j" is now supported, when true it causes a wait for group commit when journaling is enabled (instead of the previous fsync: true semantic when journaling is enabled)
• Data Center Awareness - MongoDB 2.0 allows the value for 'w' to be a string
  • The value may be a tag such as "customerData"
  • The value may also be "majority" which ensures the write propagates to a majority of nodes. We should probably make a constant for this.
  • (There may be an object support, someone needs to clarify this as I can't find documented examples)