If you frequently browse any of the main search engine forums you know that probably 75% of most search marketer's efforts are on Google, at least in terms of organic or algorithmic search.
That is probably because Google is a tougher nut to crack, and does seem to bring back the most relevant results in many cases.
Further, Google tends to account for most of the search engine referrals many sites get. But does Google really account for that many search referrals because it does a good job? Or is it because people tend to optimize for Google, and what they are seeing are the net results?