Ja ever notice? Yahoo bought Flickr in 2005. Now, before that time, you could do an image search on Yahoo and get a pretty good range of pictures from a variety of sources. Now on just about any subject, the top layer of image results will be from Flickr. Which is a great site hosting many creative photographers, don't get me wrong. But if you're looking for a picture of an opthalmologist, it doesn't do you any good to see someone's vacation beach photo where they just happened to mention the word "opthalmologist" in the caption. It's another example of being synergy wise and use foolish.
*Also a wonderful song by Dr Teeth & the Electric Mayhem.