Code review comment for lp:~tim-simpson/nova/multiple-notifiers

Tim, the code looks good. However, can you give me a hypothetical use case where someone would need to do more than one style of notification at a time? I'm not necessarily opposed to the idea, but I would like to minimize the burden of notifications on Nova if at all possible. That's why we're writing an application external to nova to aggregate and distribute notifications in a granular way.