I've noticed the same thing. One of my startups targets an audience that is less tech-saavy than normal (teachers/parents) and Bing/Yahoo AdCenter is my predominate source of traffic. I have the exact same ad/campaign running on both AdWords/AdCenter and the latter generates more traffic at a cheaper CTR and CPC. The trend holds true for organic search traffic as well. This demographic still loves using Yahoo/Bing.
