Perhaps the solution might be to allow members to permanently 'flag' threads (either a logo/bullet or colour change) to mark threads they have no interest in or, indeed, wish to find easily (in the same way that threads read change colour until the next comment is made).

This would have the same effect for Kat as having the treads seperated, she could flag the unwanted threads then ignore the red* ones leaving the rest open.

Just an idea

W

* Or whatever colour