A post on orgtheory about a seminar talk has led to a discussion thread about the appropriateness of blogging seminar talks. I offer my reaction there. I think a pithier statement of part of my stance is "If it's vitable, it's bloggable," meaning that any scholarly product that can be reported on somebody's CV is something that can be blogged about. "Invited presentation at xxx university" regularly goes on the CV, and thus is fair game, at least by default. The allowance I would give for a "research seminar" versus a "department colloquium" is that with the former one should--at least under most circumstances--respect some kind of statement like "Please do not engage in public commentary on this paper without the author’s permission." The default, though, is that it's bloggable.* A colloquium, on the other hand, is in my mind just like a conference presentation, where asking the audience to refrain from public commentary is an out-of-bounds request.
Northwestern sociology has a colloquium in which the department takes much pride. I assure you that if I feel like blogging about something that's presented there, I will.
Also, I just feel like I have to restate here: Public discussion about sociology ideas and about projects on the leading edge of the discipline is a good thing that should be encouraged as much as possible.
* At least if the presenter is a faculty member.