I've been looking at this issue as well, I ended up making a few modifications in the following template bits to hide the option:
User Control Panel -> notificationsForm
Global templates other -> likeSetDialogue (see the $freq foreach loop)
I also think these bits of code are related:
"Topic preferences" section around line 2178 in admin/applications/members/modules_admin/members/members.php
Switch at around line 92 in admin/applications/forums/modules_public/forums/tracker.php
I did not try altering this code though and can't recommend it!
I'm sure somebody is going to tell me this was a bad idea but this also seems to work for me as a forceful method of switching all instant ("immediate") notifications to "daily", "offline" or "weekly":
UPDATE `ibf_members` SET `auto_track`='daily' WHERE `auto_track`='immediate';
UPDATE `ibf_core_like` SET `like_notify_freq`='daily' WHERE `like_notify_freq`='immediate';
I've just upgraded from 3.1.4 to 3.2.3 and people are complaining that before the upgrade whenever you click on a topic that you've read before but had been updated since you last read it, it would take you to the page or post that you had read up to. Now it always takes you to the first post on the first page.
I understand there's a little round icon to the left of the topic on forum view which you can click, but you didn't used to have to click that, it would always do it. Can the old way be re-enabled somehow, without adding /unread to the end of every link?
EDIT: Looking back at another IPB 3.1 board I think they're actually mistaken and just confused about the new position of the "Go to first unread post" button, so I'll move that and make it more prominent. You can delete this topic, sorry :-)