Why is it such a bad thing to post to an old thread? I can see if you post to a time sensitive thread four years later, expecting a response it could be bad (Like "Item for sale" or "Looking for crew for this trip") but the vast majority of threads are not time sensitive and every one would agree that you should search the forum before posting a question.
A question like "What is your opinion for product X" is not time sensitive, and people for many, many years to come may be looking for input on the item specified, or giving input as there item ages. Personally I like to be able to find this information all in one place when I am researching something.
Here is a great example....
http://www.sailnet.com/forums/gear-m...p-coating.html
I had never heard of Durabak until this weekend, so I came to Sailnet to find out more opinions. This was the first thread I found. Sure, the guy responded to a "Five years, eight months and eleven days" old post, but the information is still relevant. Not to the OP likely, but to us coming along later. researching.
Also, I have found really interesting topics that where drug up from the depths of the archive by someone, about things I had not hear of, just because they added more info at a later date.
My opinion is add relevant information to a post, no mater how old, as long as the information is not time sensitive.
Some other technical forums are adopting this approach as a whole style of forum. Stack Overflow, for instance, really tries to consolidate topics into one thread, and then order the responses by relevance by a voting system, rather then in a conversation style atmosphere. I do not think that approach is so good for building community, and would not work everywhere but if there was a way to foster that process here for how-to or product review type of questions, I think it could be good.
Searching for Durabak, I got 30 results to sift through to get the gist of peoples experiences. A single topic of Durabak Reviews that people feel they can add too at any time would be most helpful. Unfortunately, the "old post" bashing discourages this. I would rather see an attitude of search first, and if you can, add your comment / question to an existing thread, keeping the conversation together, even if it spans a large amount of time.
Anyway, just my little $.02 rant...
Have a great day!