Usability is so critical to Building better b2b, that I'll just defer to the experts.
Jacob Nielsen has been researching and writing about usability since the days when web pages needed to be designed around access speeds of 9600 Kbit/s dial-up connections. His web site www.useit.com is still - in my humble opinion - the best source of no-nonsense information on the subject.
The Nielsen Norman Group is Jacob Nielsen's vehicle for conducting formal user surveys, for publishing and for training.
There you will find the B2B Website Usability report - the best single document, providing the answers needed to build better b2b. [No, I don't get commission, but this is an absolute must buy and great value for money at USD 198 for a single copy and USD 398 for a company-wide right to copy licence]
The report makes three claims that I concur with 100%
Nielsen Norman regard and structure their Customer Activity Cycle a little bit differently to the way that I draw mine, but they give a very strong message that these cycles and supporting scenarios (Bob, 52, chief purchaser at OEM Widgets, married, two kids) and are the way to go, if you want to build better b2b!