There are two processes that do most of the work for Now X. They are "Now X.app" and "Now X Agent.app". You can see these running in the Activity Monitor application (/Applications/Utilities/Activity Monitor.app).
Beginning with PB2, when you force quit "Now X.app" it will automatically quit "Now X Agent.app" as well.
NOTE: Now X stores its data in an ACID compliant database
so that force quitting the agent shouldn't cause data loss for data already saved into the database.