I've seen a lot of forums that auto-lock threads past a certain age. Sometimes it's as early as 90 days, sometimes it takes a year. I'm sure there's a plugin for vBulletin (if the functionality isn't already built-in) that would allow this, and it might be a good idea to help thwart zombie threads. Just today someone posted something about waterless cooking in a 7-year-old thread. No doubt they arrived here from some esoteric search phrase, but if the thread was locked, this wouldn't have happened. And while this is really ultimately an annoyance at worst, there have been a few threads where people chime in on suggestions from five years ago. I recall one (don't have the link) where someone posted something like "I'm having the same trouble too, how did you solve this?" to someone who hasn't been logged on in ages. I've also seen a few forums that actually mark old threads as "ancient" or display them in a different color. That way, readers know that the content in the thread is very old and may be outdated / unreliable. This would be especially helpful given how much has changed in our subject area in the past few years. Just my judgment-free $.02.