Just given it a try. Can't say I find it all that useful (though maybe others will find a use for it), as it shows all the posts by all the users in my list, but in chronological order, which means they're pretty much thrown together randomly as regards the threads they're taken from. If I just want to see all posts by a single user, that functionality exists already via the user profile.
The way I understood Sin's original post (and what I also think would be useful) was as a request to hide individual posts in a thread. For instance, the thread
Hair salons / ladies' hairdressers contains many useful recommendations, but interspersed with lots of posts like "Yoo-hoo! I've got an appointment for tomorrow!", "They aren't answering the phone - are they closed today?", "Do they do hair extensions?", "There's a good salon out in Pasing" (other end of the world for me). It would be great if I could block out all the stuff that is irrelevant for me, and reduce the thread to a concise reference list of hairdressers that are of interest to me personally.
Note that this doesn't mean blocking individual users, as some of a user's posts might be useful, while other posts by the same user might be unwanted fluff.