My Mom uses yahoo. She is 60. So I would say that people who are not as computer savvy use Yahoo! probably because they have seen the Yahoo! commercials on T.V. Bison
yahoo also brings decent traffic and it is easily to show on top pages compared with goolge which is strict. (that's why google become no.1?)
The new generaton is using Google. and the older genearation did not switch to Google. So, if you like to go by age, below 35 Google and 35+ Yahoo That is my strong assumption. Thanks