In my experience, the feature does a pretty good job and doesn't adversely affect performance in a noticeable way. No doubt it will exhibit some silly choices, just as those automatic ad-generating systems sometimes do, but it might be worth having anyway.
the #1 thing that jelsoft needs to do is better their search features in vbulletin, because it annoys me even on my site which has less posts than this site has members. So it aggravates me to no end here.
It would be great if this list could pop up, say during a new thread post.
Once the post is titled, you'd have the ability right there to "search for similar topics"
...kind of like the "have you searched before starting this thread" reminder that was suggested before, although I think this would work better because it will be perceived as a feature rather than a reminder.
That said I know nothing about the forum software...so it might not be workable.