That said I'm not sure I agree with Mark's reasoning. If they are failing to raise a smile, then fair enough. But I don't believe that one spoof post a year diminishes the academic reputation of blogging. After all, many of the well respected papers have, and still do run April Fool's day stories, as do the BBC.
However, I do agree that it detracts from blogging's reputation when blogs all too frequently intersperse their more academic-related posts with those of a more personal nature, or which are more off topic. For me, family stories (except the more important ones) and views on the run up to elections, or this year's MTV awards are all best left alone. I guess that this is what Mark means when he talks about "decline in the academic quality of the biblioblogs". Mark models this very well himself, reserving his Dr. Who related posts and so on for his Resident Alien blog.
That said, I suspect I'm not even taken that seriously by the majority of academics inside the blogosphere, so the chance of me ever gaining respectability with non-blogging academics is pretty remote at best.