The email notifier always sends the notification with the same exact subject line. As a result gmail bundles them all together as the same "conversation".
So after only a few days being subscribed to some tag set I get this in my inbox:
Since I have a filter to label such messages and skip the inbox, and since I (like many users) don't delete messages but archive them, the end result is a DOS attack on my gmail :)
It's 14 by now, but will probably grow very big very soon.
The easy fix is to add a date to the subject line.