Librarians have always thought in blog format, in my opinion. Not necessarily as a journal tool, but as a place to record useful bits of information to share with patrons without having to go through a webmaster or committee to design a page on the net. Of my 16, 4 are fairly frequently updated, and two of those are my personal ones (librarian-related and my cancer blog). Two others are pretty much defunct, but kept on my dashboard as a record. Another one was done two years in a row for a national library conference roundtable - no idea when that one may come in handy again. One is a project with another cancer blogger that has not been fleshed out yet - left on the dashboard in order to keep the domain name current. Another 7 are blogs that I created and maintain for undergraduate workshops at our university that link to resources available to anyone on the web, since the visiting students don't have password access to our library's digital collections. I refresh the undergraduate blogs once a year, but check them once a month to make sure the links (mostly to government sources) are live, in case last year's students are still using the blog as a jumping off point for their current research.
Finally, one was created simply as a bibliography for "After Our War", a 2007 UNMC CE course designed for Nebraska physicians and mental health professionals.
Depending on what you are blogging about, I don't think you can have too many going. If I expected to add to or edit all 16 in one week, that would be way too much. But I have only 4 that need frequent updating - and since half of those are personal, that is a reachable goal.
A few of my blogs that might be of interest: