After doing a little searching around, I was surprised to see that this hasn't already been suggested.
Currently, on a forum I am active on that runs XenForo 1.3.2, I've noticed that profile posts can be a little annoying. Every time a user comments on a profile post made by any user, I get a notification for each and every response in the comments, which in some cases can generate several notifications for the same profile post.
I suggest to add similar behavior to replies to a watched thread, where you receive the first notification for the profile post until the next time you open that profile post and view the comments. This would decrease a lot of notification spam for forum owners or administrators who want to keep notifications on for their profile without receiving pages of notifications for profile comments.