It
can work depending on your particular site as long as the majority of searches are repetitive. If new search words/phrase combinations make up the majority of your daily searches however, you are going to be spending a shitload of time assigning ads to them... not to mention slowing the site down as your database/mod rewrite list expands exponentially.
If it's worth your time to get that manually involved, you might as well make a new page/post based on that search or better yet create it on the fly.
