I've mentioned it before, and I'm not alone. (STOP! Ask yourself this: Are you on company time right now? Is reading AdvisorBits really a part of your job description? ... This post? Why?) While it is arguably a powerful business tool, the Internet presents a whole new series of challenges for managing the modern workforce. When a computer's memory gets too full it may try to use space on a disk. Sometimes there's just too much moving in and out of memory and it causes disk thrashing. I agree with Kathy Sierra that there is a similar phenomena, called Brain Thrashing.
The Internet is filled with distractions that have nothing to do with getting work done, and in fact even some things that seem on the surface to be productivity boosters can in fact cause the opposite effect. I enjoyed reading more about this issue in a larger context than my own experience over at Internet News in an article by Mike Elgan.
I think he is probably right on about his primary assertion, and I only wish I could get 6 hours per day with total focus on a productive task.