I have two blogs that I have upgraded and one still on 1.5. Since I upgraded the two, they're both having problems with the "more" tag. I've been getting e-mails from all of my writers saying the more tag does not save when the post is published. I then log in to manage the post and when I publish it saves with the more tag enacted.
Bottom line is that since I have upgraded my admin accounts are the only accounts that the more tags saves in.