As a buyer point of view, it's very hard to find a new post, most of the time the same "hot" items will occupied the first few pages. Also suggest for different items, should create a new thread instead, in that way, it's easier to search. I think previously most of us will park under a same thread so that it's easier to monitor (selller).
As a seller, it's easier to manage if the communication is via PM, SMS, phone or email (although you can stated that in the thread).
Apart from that, i found that some of the users like to give their personal comments about other people item and pricing, for example, "there is one that sold for XXX amount in other thread...", or "new one just cost xxx amount in US etc..." i don't think those comment are helpful and most of the time are based on wrong information or without looking at the condition of the items.