I think Michael Calore (with Scott Gilbertson) really nailed it in this post today on the Wired Blog:

I’d hardly be called original for suggesting that vertical searches are the future of the internet, but it’s offerings like Krugle that remind you why everyone touts vertical search engines. I have no doubt that a generalized Google search will always be useful for some, but increasingly, to really find quality results, you need to narrow your searching pool. Searching a subset of the web — Code, Blogs, News, Medical, etc — is in the end perhaps the only way to make sense of it.

SEO master Eric Enge of Stone Temple Consulting asks “Are Vertical Search Engines the Answer to Relevance,” in his recent post at Search Engine Watch. He quotes Outsell reports as predicting the vertical search market will reach $1B in revenue by 2009. My guess is that this is way low. I believe vertical search engines will do to the horizontal giants what cable television did to the broadcast networks. Cable eclipsed broadcasting’s revenue by the late 1980’s. Moguls were created and empires built, with cable networks becoming the among the largest media firms in the United States. At the time, the networks laughed at the vertially oriented upstarts with their niche focus on specific verticals, calling CNN the “Chicken Noddle Network,” stating with confidence that only major networks could be trusted to do news.

Eric does an excellent job of delineating what it is that horizontal search can’t always and what vertical search engines do so well. To paraprase: vertical search sites “know the context.” Horizontal search engines do not know what you want based on your search query. For example, if your query is “surf” and you live in Santa Cruz, what is it that you really want? Or if you type in “diabetes”, are you a doctor looking for research data or a patient looking for treatment information?

Vertical search solves this problem in that they are designed for a specific purpose. If you decide to use a search engine called “Health search engine for doctors”, instead of one labeled “Health info search engine for patients”, you reduce the ambiguity of search queries even before you type in your query. And vertical search engines know their target audience — often a mystery to the horizontal search engines.

A new version of last year’s white paper The Emerging Opportunity in Vertical Search is now available for download. It is free (if you register on their site) and provides a good overview on vertical search engines. The paper was written by e-media consultancy SearchChannel and Slack Barshinger and talks about some of the trends behind the growth in vertical search engines. It covers some of the advertising models used and expands its listings of vertical search engines from the first version.

One important issue vertical search engines address is getting at information that horizontal search engines miss - either because it is out-of-reach of their crawlers or the format of the data is too complex. Chris Sherman addresses this in a paper called The Invisible Web.

Chris points out that horizontal search engines can’t index something where there are no links pointing to a page that a search engine spider can follow. Or, pages may consist of things horizontal engines don’t index - graphics, CGI scripts, PDF files, etc. But the largest miss is information in databases. Indexing spiders stop at the front door of these libraries, getting the address but nothing about the books, magazines or documents inside. And there are thousands, perhaps millions, of accessible databases untouched by horizontal search engines. Is the data easy to get at? No, not always.

Very often it is this special skill - the extracting of very important information and presenting a highly relevant result in response to a search - that makes vertical search engines so valuable.

What do you think? Is this a problem horizontal search engines are working on? Will they be successful? What are some examples of vertical search engines that are doing this well?