I'm involved in managing 8 business to business campaigns. In doing so I had an early preference for Yahoo over MSN or Google.
MSN seems biased towards young consumers. Google, because of its academic roots and "do no evil" philosophy seemed to produce SERPs that were (relatively) biased against traditional business websites.
See the example for the term "Fulfilment".
"Fulfilment" on Google.co.uk
"fulfilment" on UK.Yahoo.com
The problem is, that as Hitwise has recently reported, Google's UK market share is about to break through the 75% barrier. Squeezing MSN and Yahoo into ever smaller territory with about 7.5% market share each. As a search engine marketer involved in B2B my observation is that the switch to Google has been even more severe.
12 months ago Yahoo regularly achieved 15%-20% of my B2B clients' traffic. Today that share ranges from 1% to 6%. That is, it is below the share Hitwise
says they have in the general market.
Does this mean that corporate web users have flooded out of Yahoo? To my mind, as the example above shows, Yahoo provides a superior product when it comes to relevancy in many corporate categories.