If there is something that identifies knowledge workers from the rest of the working set, maybe it is this: That knowledge workers control how they manage their time and activities. This is more of an effect of the shift to knowledge work than a definition.
Jerry McGovern has a related article in his weekly New Thinking newsletter: Are you too busy to think? (September 27, 2004).
He talks about a topic that affects a lot of people, particularly those who like to think for a living.
There are certain words you need to ban the use of, and "busy" is one of them. In knowledge-driven economies, "busy" is an outdated word that reflects a manual labor approach to work. Instead of "busy" you need to use words such as "effective" and "productive".
This brings to mind is the idea that we prioritize the things that are important. While obvious, this appears in interesting ways. Do you claim to not have time to [fill in the blank]? Even when it seems important to others? This is an example of your priorities taking hold and helping to make decisions. Do you have trouble remembering names? One could argue that it isn't important to you - that you have other things that absorb those capacities. Conversely, if it is important, you can learn how to remember names.
Of course, this characterization isn't always accurate. Maybe it is just easier to do the simple things, leaving those big items for later, "when there is more time." But then, when I look at my behavior, procrastination is all part of the prioritization game for me as well. If it is important enough, it gets done. This is one of the reasons I find value in bouncing ideas and problems off my friends and advisors. I frequently can't get through them alone.
Near the close of the McGovern article, he says, "If you want to have a successful future, you must learn to become a better manager, both of yourself and other people. " Perfect.