It is well known, that there is a standing secret committee of academics that keeps track of all the stupid things you ever said.
The Permanent Record follows you your whole life and determines all things: smart ass comment in 7th grade English Lit - no tenure for you my girl? Questioned energy conservation based on a youthful fling with "alternative science"? No postdoc offer from The Institute for FuddyDuddies for you my lad. Forgot about Zeeman splitting in intro grad radiative transfer homework problem? That NASA review panel laughed all the way to the "Good/Fair" grade for your proposal.
So, why do academics blog?
Our senior colleagues despise it, for the best of reasons, they didn't blog when they were lads.
Anecdotally it will hurt your tenure, prospects for hiring and probably make your viva more painful...
Yet more and more academics blog.
Some even do it properly, tying it into their research, leveraging it into class assignments, or working it as major professional outreach efforts.
Most, of course, fizzle into dormancy.
Many are just erratic random snippets of diary trivia, occasional flurry of insight or exposition, but really nothing special.
But more do it all the time. Well, until the next hot net.thing comes along.
Well, there are many reasons... other than Ego. Or Outrage.
Most of us (me) are not Good Writers (I don't usually want to take the time to carefully proofread lite blog stuff, and I alternate between being unnecessarily crypically allusive, so that only about 3 people "get it", and only one is reading, or I use the germanic infinite nesting of conditional sub-clauses - creatively punctuated - so that you need to be a mathematician specialising in transfinite set theory to actually parse the meaning of the final sentence). I'm not actually trying to create Turing non-Halting sentences. Fortunately both of you are reading this and each of you gets a part of it.
I should do more science topic blogs - I have a memo-to-self listing about 100 to-do topics, including those sugested in e-mails, but it is hard work to do proper, and proper level, science writing - I might as well write some papers, so that is self-limiting.
Other bloggers know more politics/music/movies/electronics/etc and are better connected.
I'm not really a fan boy of much of anything, so I don't want to do monomanic blogging.
And robo-blogging (like adopt-a-blog or iPod iChing every day) could be done by script, no point except as diversion and filler.
So, why bother doing heterogenous snippets of science, poli-rants and random snippets of life?
Really? The reason to do it, in my experience, is something I noted long before blogger.com came to be, that The More You Write, The More You Write.
Blogging is warmup. It is lubrication. It is light impact aerobics.
Academia relies on writing.
I am not particularly prolific publishing stuff.
I don't need the public exposure of a blog - my research has received significant media exposure (too much, many would claim); I don't want to spend more time on press releases, at least two journalists seem to have me on speed dial and I think at least one reads the blog in the hope I'll inadvertently leak something...
Typical physical science writing output is ~ 4 medium length papers per year. That's ~ 32 pages, say 20,000-30,000 words given an ApJ page (I just did a "wc" on a tex file for one of my median length papers).
In addition there are conference papers, they are shorter and a perturbation on the main output for most people.
Then there are talks (20-40 keynote slides, text light, graphics heavy, per talk, with some recycling).
Proposals - call it 4-10 proposals, ranging from less than 2000 words for phase I Hubble proposals, to ~ 50 dense pages for multi-year solicited NASA proposals - some of which is boilerplate, so maybe 20 pages of actual new text, 10,000-20,000 words per long proposal.
And then there are lectures... a semester class reduces to ~ 100 pages of single spaced TeX'd text, excluding figures.
There's a reason a lot of lecture classes become books.
You can re-use a set of lecture notes 3-4 times, after which you better redo them from scratch or you'll be in danger of becoming One Of Those Lecturers...
So call it on average 100 pages of notes every 1-2 years depending on your class load.
The problem is, that with rare exceptions of Lucky Natural Writers or People of Uncommon WillPower, everyone gets the dreaded Writers Block.
It is a very real and very dangerous problem. Get it for many months at the wrong time (like just before your thesis completion, or late second year of your first postdoc) and it is career ending.
There are ways around it, like the infamous "do the bibliography now", but in the end there is something inherently distasteful and boring about revising and re-reading old material.
This of course is why we hate referees. Other referees that is.
Blogs are a writing lubricant. Like every lubricant they can be overdone, but what they do is provide light relief.
Blog writing exercises the mind, gets you in the mood to write. It forces you to think about a specific topic, possibly even science... It forces you to go read up on stuff. Comments sometimes force you to review critically what you wrote, or fact check.
Blogging is something to do to break the transition from proposal preparation, through code writing, to doing the dreaded referee mandated revisions... it can occasionally be fun (well, can't have that).
It takes time. No denying that.
So, if The More You Write, The More You Write, In Moderation of Course, where is the time coming from.
Well, there is the stereotype, pushed by Street Tough Real Reporters (mostly Texas A&M journalism majors...), of the cheeto munching pajama clad geek blogger with no life...
But I, and many people I know with blogs, actually have lives. Honest we do.
For me, unfortunately, the time is coming out of reading. I am reading less, given my real life constraints, and blogging is one of the factors that reduce reading time.
Which contradicts what I said before, but in a sensible way. Blogs focus reading on particular topics. I have less time now to do free association reading.
This is self-limiting. Much as giving too many talks eliminates time to write papers, leading to fewer invitations to give talks. So lack of random reading limits the input for random blogging.
Not a problem for single topic blogs, but refreshingly self-regulating for the average random ramble blog.
And here endeth the sermon.
PS if you blog, and your output is non-zero, you will say something stupid, maybe lots of stupid things.
And it is public and archived, for the whole world to see, forever.
But it really is ok, mostly. You might even still get to be President one day - 30 years from now it will be like having smoked dope in the early 70s. Embarrassing, slightly passe, but not to be seriously held against you. Just be brazen about it.