Tony Karrer gave a Web 2.0 presentation in Los Angeles to an audience at the Institute of Management Consultants (unfortunately I was not able to attend having just learned about it that day). He covers two aspects: serving clients and reaching prospects. Apparently, most of the interest was in the latter area, and as a summary of one of his theses, I reference the title of his blog post, "LinkedIn - Prospecting No - Conversation Yes : eLearning Technology".
For those looking for more info as it relates to consultants and LinkedIn, Ford Harding is one of the gurus I've looked to as a guiding light when I committed in early 2000ish to work at actively improving my sales and sales management IQ, particularly around professional services sales. Here's one of Ford Harding's posts on "Liking LinkedIn?". He has other posts regarding LinkedIn as well, so be sure to dig in and poke around if you have a chance.