Subject lines are things you put on the top of your email so that the recipient knows what the email is about, when they see it in a list. They are useful.
It's unfortunate then, that the last 10 threads on wikimedia-tech (as sorted by my mail client) had no meaningful subject line.
May I suggest changing the subject when you reply to a mediawiki-cvs post, to something somehow related to the feature or bug in question?
We manage to pick a meaningful commit message when we commit these revisions, so surely there's no reason why we can't pick a meaningful subject when we're talking about them.
-- Tim starling