I don't think so because sometimes topics are dragged up from the past and usefull comments can be made.
Auto pruners are a goo idea as they keep a forums database in trim spick and span etc... But you only really need to sea pruner if you are experiancing a massive database slow down.
although perhaps a threaded type view plain text page for old threads might be good. that way old useless threads can be trimmed whilst the opinions and/or advice can be preserved.
I think all topics should be left open.The world of computing never stands still and there is always something on the way that can change a situation. For example, if users are discussing a security hole and a patch is released later, it would be good to put a note in the old topic.
Lol - well I think I do it as well as is physically possible. Do you not realise the number of posts on this Forum in one day? I probably look at about 80% of them!