- Writing an article is a lot of work: will the benefits make it worthwhile? (Ad revenue would help with this.) The benefits of name recognition may be tough to quantify before you reach real renown, for example.
- A picture and biography of the author raise questions too: playing on their book analogy, I do check the dustcover occasionally, but it's rarely the deciding factor; particularly when I'm looking for an authority on a subject (as opposed to reading for pleasure, for example): the calibre and number of recommendations, followed by the quality of the writing are much more important to me. Also, I tend to agree with the criticism of journalists who include their pictures next to their newspaper articles: shouldn't the writing speak for itself? (Although, admittedly, this does seem fairly innocuous nonetheless.)
The circumstances surrounding Nupedia leave me of two minds: one could say that Wikipedia's rise detracted from Nupedia by offering a potentially less time-consuming means of contributing. However, one could also say that Wikipedia's rise brought attention to open knowledge in general, and that experts would quickly recognize what many more people have since: there are limits to the utility of articles that are perpetually open to modification by all; a sister site with Nupedia's philosophy could be attractive to that community of experts.
Whether Nupedia implemented that philosophy is open to debate. Certainly, and I say this with a tinge of irony, its Wikipedia article details a number of flaws. For my own part, I was content to copyedit articles in my subject area of computer science, so I have difficulty believing that experts suffering comments from anonymous reviewers with no knowledge of the subject area was endemic or little more than 'growing pains', as it were. Again, I know I had doubts as to whether I would be accepted as a CS reviewer with only a BCS to my name.
I'll be watching 'knol' with great interest. In addition to the tarnish Wikipedia has accumulated in recent years, the other, probably far more significant, circumstance associated with knol's introduction is its sponsor, and the enormous buzz that comes with it. Many will rightly say that if Google can't do this, no one can for the foreseeable future.