Currently, 83% of our total traffic is from search engines, or rather, one particular search engine:
Search Engine Visits 3,417,919 Yahoo 9,779 Live 5,638 Search 2,961 AOL 1,274
[...] Google delivers 350x the traffic to Stack Overflow that the next best so-called "search engine" does. Three hundred and fifty times!
I'm not sure that there's much I can really add to that, except perhaps a quiet and dignified "Holy crap!".