"So-and-so has added you as a friend"
It's right here: http://www.insanejournal.com/manage/subs
I think that the "all comments in my journal on any post" option will copy your own replies back to you in email; if you're getting comment notifications okay, leave that one alone. ^__^
So far, all I've done is go back to LJ and see what the web address is for those useful things, then add the necessary stuff to the end of the InsaneJournal addy -- and so far, it's worked like a charm.
ETA: The thumbtack feature to keep track of posts et al is found when you actually click on a cut/view comments/otherwise go to the actual post. It's right there in the little toolbar -- just like on LJ.
caoilainn