I don't agree with the idea of autolocking old threads. I participate in a lot of forums, and I've never seen one that needed such a system. Educating the board participants to only post in a thread if they have something relevant to say, and post a new thread if they have something new to discuss, is the better route.
Yes, if you leave threads open, you get things like what happened this morning, where a guy posted in the Uniden 3.01 firmware thread asking (essentially) how to program his new 396 with the data from his 246. But that's not because the thread is open, it's because people don't know enough to post a new thread (or search properly for an old one) for their own question/issue.
However, if you auto-close a thread, even one that may not have had a post for a year, you then prevent people from contributing if something new is learned. As an example, Alberta scanner users discovered several years ago that scanners could not trunktrack the City of Red Deer system because it has an oddball band plan. When the custom band plans were introduced in whatever firmware update Uniden pushed it out in (2.x or 3.x, I forget), the information that this problem had been fixed would have been impossible to post in the existing thread, because the thread would have been locked. And starting a new thread just to announce this would potentially miss the people who had subscribed to the existing thread, expecting a response there.
Again, I don't think the answer to the problem of people reviving old threads without new/beneficial information is properly rectified by locking all threads. I maintain that it's a training issue.