Presentation of Search Results is key.

Tamar Sadeh from ExLibris touches a very important point in her article "Google Scholar Versus Metasearch Systems" onHEP Libraries Webzine Feb 2006

"Beyond searching

Google Scholar may provide an easy way to search. However, with the constantly increasing quantity of scholarly data, Google Scholar will soon be facing a new challenge, as will database providers and metasearch systems: the comprehensive presentation of search results to the user.

The assumption underlying the implementation of relevance ranking and its use as a sorting order is that end-users will not scroll down and scan large amounts of data. Therefore, the results that are most likely to suit their research needs should appear at the top of the list. However, this sorting order has several drawbacks. As mentioned earlier, users have different research needs, and an item that is most relevant to one user may be less relevant to another.

Another problem with presenting search results in any type of linear list is that sometimes there are a great many results. Some users, particularly those who are novices, may not know how to define their queries effectively; however, once the system analyzes the set of results and provides options to narrow down the list, such users can easily drill down to the relevant subset of results."

That's one of the reasons that we implemented faceted searching in Engineering Village. Tamar gives Vivisimo and FAST as companies which are custering search results.