[Logician]

I think the ability to contribute to an old thread is the distinguishing feature of a bulletin board and makes it preferrable over mailing lists.

I admit that sometimes user do it without realizing the thread's date so it would nice to make thread date more obvious in these threads (which my "blink date if thread is old hack" does in my own board). But as a general I don't agree with any restrictions (like closing them) that will discourage replying to old threads.