I've been very fortunate. My various employers have not only understood and accepted, but even to a certain extend expected that I have an intellectual life of my own apart from the day job. So when I decided to start blogging, I also decided that I would not take particular steps to conceal my identity. (Indeed, I recently renamed this journal from nhw to nwhyte in order to make it even clearer who I am.) And, perhaps surprisingly given the number of people who hate the work I do, I have never had any serious blowback from it at all. Of course, I'm not posting slash (or even het) fics here, and if I am doing so elsewhere I am certainly not going to link to it in any visible way from this account.
I am also restricted what I can say in a public forum even on non-pornographic topics. By the nature of my work, I am privy to a lot of stuff that needs to stay off-line. I have professional relationships which I cannot put at risk by posting about them here. Though I have to say that I think most people with jobs are in a similar position, including, say, the guy who blogged about how crap his temping job was at company X (and named the company), or the barmaid who blogged about how badly her celebrity customer behaved. That strikes me as stupid behaviour, and the fact that they both got sacked is pretty inevitable.
There are ways around it. Livejournal's locking and filtering can be a useful mechanism for venting about the shitty day you've had at work (which in my case, I'm glad to say, are not very frequent.) La Petite Anglaise famously got sacked although she had discreetly maintained her own anonymity and that of her employer; she won substantial compensation for unfair dismissal. Others seem to get away with more.
One of the reasons I keep adding to my own on-line presence in my own name is to try and drown out the occasional hostile commentary I have picked up (and which I also link to in embittered, locked, filtered entries) by ensuring that most of the stuff that comes up when you google me is stuff I've written or consented to.
I have of course set up google alerts on myself; the other week an Irish blogger completely misquoted me on a sensitive issue, and I picked it up and demanded (successfully) that he delete the inaccurate paragraph. I was probably the only person who actually read the entry in question, but I felt it worth putting energy into; once it's online it's in the public domain.
Online anonymity is going to become increasingly difficult to maintain. I routinely google shortlisted candidates whose CVs hit my desk, looking for evidence of political activism (which, from where I'm sitting, is a Good Thing). Is that an invasion of privacy? I think it's due diligence, as long as you treat the results of your googling with a serious reliability filter. If a candidate isn't on Facebook these days, I tend to wonder why not - indicates a lack of interest in new technology and networking which is rather surprising for someone looking for a job in my line of work. (There is a Facebook group for my growing number of ex-interns.)
But I entirely understand why many people whose personal or professional circumstances are less favourable than my own choose to try and maintain on-line anonymity. (And, as stated above, I recognise that my own choice cuts me off from certain topics, at least using the identity of nwhyte.) I won't add people whose real names I don't know to my most private LJ entry filters, but otherwise I don't really care what degree of anonymity you choose. I may mildly regret some choices - thinking of one person in particular whose friends-locked list of livejournal entry tags is in itself tremendously entertaining reading! - but I respect the fact that they are made for reasons which I have no right to inquire into. edited to add: And if you are an pseudonymous user who annoys me or my friends, I promise I will not devote any energy to exposing your real identity, because two wrongs do not make a right.
We all have choices to make; and they are new choices that previous generations did not have to make.