As of this writing, there are 47 million professional profiles on LinkedIn. How many of them represent your prospects, future partners, or happy customers just waiting to write a testimonial for you? After 6 articles on the topic you now have no excuse not to find out. :o)
Strategies, a LinkedIn profile guide, a LinkedIn feature guide, case studies and many user and reader contributions:
Maisha Walker's Inc. magazine series - a Small Business Owner's Guide to Leveraging LinkedIn