According to a BMJ study, Google searches revealed the correct diagnosis in 58% of cases published in the case records of the New England Journal of Medicine in 2005. In each of the 26 cases studied, researchers selected 3-5 terms from each case and did a Google search without knowing the correct diagnoses.
In conclusion, "the use of web based searching may help doctors to diagnose difficult cases."
Many clinicians use Google on a regular basis to look up information, to supplement their knowledgebase or inform them of the latest findings on a particular disorder or drug. But most physicians who use Google in its current form at least, would not let a search engine (which basically relies on "wisdom of crowds") become a trusted diagnostic adviser.
The media has had a field day with this. You judge for yourself.
Googling for a diagnosis--use of Google as a diagnostic aid: internet based study. BMJ.
Is Google The Fastest Diagnostician On the Planet? UBC Academic Search - Google Scholar Blog.
This is research? BMJ. T C Winthrop.
Google 'aids doctors' diagnoses. BBC
Google in Medicine