A modest proposal
Let's look at a search referral traffic the way a site owner would.
I picked a basket of medium-to-large websites and looked at the inbound search traffic percentages using Hitwise. I included Topix in this mix, both because it's a representative content site, and also because I could double-check the Hitwise numbers against our own server logs and 3rd party measurements from Google Analytics. As it turns out, the relative inbound referral ratios agreed between Hitwise, Google Analytics and our own server stats.
What I did
I did a simple average of the percentages instead of a weighted average, to offset the chance that a particular site was being unduly favored by a particular engine. (It doesn't look like that is happening though; both Yahoo and Google favor Wikipedia and IMDB in their top organic outbound referrals, so they seem to be sending traffic to the same kinds of places in their listings). These numbers probably undercount Ask, because they were below the top inbound referrer cutoff for some of these sites.
I'm not a professional analyst, and my approach here is pretty back-of-the-napkin. Still, it confirms what those of us in the search industry have known for a long time.
The New York Times, for instance, gets nearly 6X as much traffic from Google as it does from Yahoo. Tripadvisor gets 8X as much traffic from Google vs. Yahoo.
Even Yahoo's own sites are no different. While it receives a greater fraction of Yahoo search traffic than average, Yahoo's own flickr service gets 2.4 times as much traffic from Google as it does from Yahoo.
My favorite example (not included in the above stats): According to Hitwise, Yahoo blogger Jeremy Zawodny gets 92%
of his inbound search traffic from Google, and only 2.7% from Yahoo.
"We see little to stop Google from reaching 70 percent market share eventually; the question, really, comes down to, 'How long could it take?" -- RBC Capital Markets analyst Jordan Rohan.
Welcome to the future, we're already there. To paraphrase an old industry saying about IBM...
Google's not the competition, Google's the environment.