We know that experience makes you a better searcher. So if a lot of people ask for something, search tools respond accordingly. That is what AskJeaves is all about in their 'answer the question' database. So most of the Web will remain invisible via the typical search tools. The key point in finding this information is using more than one of these resources just like one needs to do when using typical search tools.
Familiarity also breeds expertise.
You mean offline tools. I mean tools that are designed to search the Invisible Web. One last point. It also helps to subscribe to a variety of newsletters to stay current. Cindy Coan A conference session bib.