Enquiro have just released a 'B2B Purchasing Behavior Whitepaper' based on a survey of over 1000 B2B buyers, I haven't had the chance to read it fully yet but I usually like the quality of research from this SEM based in Canada. Basically the summary is that online is now far more important than offline in the purchaser decision making process, with 70% of users using search engines as a primary research resource, and Google remaining the first choice for B2B purchasing research.

"Enquiro's research paper shows that when it comes to business to business buying decisions, online influences such as vendor websites, search engines, and industry information websites are surpassing offline influences such as word-of-mouth and trade publications"

Confirming what most of us know already about position being a big influence over interaction (although volume in and of itself isn't for everyone and brings other issues and doesn't always stack up in the ROI stakes):

"The top four organic listings captured 52.6% of all the click throughs, with the number one organic result capturing 27.1%.  Position again proves to be important in the sponsored listings, with the top pay-per-click ad capturing twice the number of click throughs as the number two ad (7.4% versus 3.4%)."

http://www.enquiro.com/Downloads/b2b-research-2007.aspx