I am signed up with about 200 companies. I work for 30-40 in a year and make 90 percent of my fees from about 12 companies, plus reimbursement only from about 6 more (hair care, oil changes, etc.) HOWEVER, about once per quarter, and always in Jan and October (the starts of many MSC'sfiscal years) I check just about every web site. This is because clients tend to move their accounts in October or January, depending on their fiascal years.
Every year, I have also found at least one additional company that I ad never heard of, signed up with, and then made substantial fees from them. In 2011 that was a company that made up almost 20% of my fees for the year!
Sooooo, always be on the alert for changes and new things that will make money for you. That means maintaining at least some communication with many, many more companies than you may shop for routinely, AND haunting the forums for mentions of new companies.
Based in MD, near DC
Shopping from the Carolinas to New York
Have video cam; will travel
Poor customer service? Don't get mad; get video.