"In science, the distinction arises when one wishes to short-circuit the process by which the expert demonstrates her expertise by providing the interpretive narrative and rationale by which she has arrived at her conclusions. Once one moves on to the "just trust me on this" or "well, my professional experience and judgment lets me know that ...." argument, it becomes an appeal to "authority" for authority's sake, as opposed to an appeal to the experienced individual's actual related expertise."
One would think this would be self-evident, especially to bloggers professing to be scientists of great "authority". However it was none other than Greg Laden who kicked off the whole discussion with commentary following Kamel's recent post on anonymous blogging. Laden seemed to be arguing that anonymous blogging is a bad thing because one is unable to assess the credentials of the speaker, and therefore unable to determine the validity of their arguments.
I've said most of what I have to say on this topic in the comments to Kamel's post and over at DrugMonkey's place. Here I'll summarize by saying I tend to think that the validity of an argument has to do with evidence and reasoning, and not how many degrees or prizes the speaker has won. An accurate statistic quoted by an anonymous blogger for example, is no less accurate because the identity of the person citing it is unknown. Likewise, it is no more likely that HIV is not the cause of AIDS just because Kary Mullis won a Nobel prize for the invention of PCR.
But that's just my opinion.
UPDATE - Greg Laden has now posted a clarification of his position on anonymous/pseudononymous blogging at his place. Go there to read his opinion for yourself.