Did you know that if you search the major engines on the Internet, then you will find very little overlap between them.
. . .the percent of total results unique to only one of the four Web search engines was 84.9%, shared by two of the three Web search engines was 11.4%, shared by three of the Web search engines was 2.6%, and shared by all four Web search engines was 1.1%. This small degree of overlap shows the significant difference in the way major Web search engines retrieve and rank results in response to given queries. (Information Processing and Management, 2006 (from: http://sky.fit.qut.edu.au/~spinkah/eprints/IPM-OverlapStudy.pdf. This means that for quality research, you must search Google, Yahoo, and Microsoft Live (or Bing) so you don't miss anything!
Another way to visualize this more clearly is a free search tool called SEOChat. You can read a brief web article called How to Visually Compare Google, Bing, and Blekko Search Results. Here’s a snapshot of a search. Each dot represents one search engine result for any given search.
Essentially, the more blue you see, the more overlap you have and less of a need to use other search engines. This is a high level academic search. As you can see, there is not much blue. Notice the percentage of overlapping links is 16%.
You are probably thinking, “This is an academic search. I would expect academic searches to have fewer overlaps. So what about a more generic search?” OK. Fair question. Here are the results from a more generic search for the term “gardening.”
The problem is that Google’s effective marketing suggests that they have indexed the world. This would not seem to be the case – even on a generic search even though the overlapping rate is slightly higher.