X-Livejournal: itemid=133 talkid=38 journal=lusers:9 postby=joe commentby=jane:1 parentby=kathy
This indicates that Jane (who is your friend, with groupmask 1) posted a comment (talkid 38) in response to a comment by Kathy (who is not your friend), in a thread started by a post (itemid 133) from Joe (who is not your friend), in the lusers community (which is on your friends list, with groupmask 9).
What you do with that information is up to you. Personally, I'm going to write some procmail rules to send comments by friends into my main inbox, and other comments into a mailbox that gets checked somewhat less often. Others might want to completely discard comments that aren't directly in response to their comments or posts. Others might want to pop up a browser window when they get a comment in their journal from their SO. Whatever you want.
The entire subscription/notification scheme needs an overhaul, but that's a larger project. :-) This is a quick cheap win.
I also made a small change to the subject lines that get sent. Before, if your post was on subject "Squirrels" and I commented with no subject, you would get an email saying "Reply to your post..." Now, you get an email saying "Re: Squirrels". You only get the uninformative "Reply to your post..." if neither the poster nor the commenter used a subject line.