Currently, the default for users is to receive an email whenever someone changes the settings of a group they are a member of.  This seems like a great way to spam users!  It would be nice to allow for administrators to change the default messaging settings for new members.  

Related to this was the ability to throttle the number of emails coming from the Hub.  So, for example, send only one email in a 5 minute period so that quick changes to group settings don't send tons of emails.

- Drew