By all means blog about the work you do as long as it is legal for you to do so and not a horrendous breach of contract (minor breaches of contract are generally overlooked). But never blog about your colleagues, remunerative packages, employers, or specifc working environment. General observations about say, finance or software companies are ok, specific mentions of why you would like to re-arrange the cubicles in order not to smell coffee in the mornings or to avoid the view of your manager's ass-crack not so much.
There have been multiple incidents in recent years of people being fired from their jobs due to highly publicized or particularly popular blogs. While this is extremely rare it does happen, and even the smallest negative mention of a workplace can trigger the overreaction from a company. Even if 90% of what you write about is completely unrelated to your workplace, if tipped off to the fact that you have a personal blog that has ever portrayed your company in a negative light, your employer will find the other 10. Or more likely their lawyers/HR assholes will.
This will almost certainly never happen. But why not make it an absolute certainty? Never blog about your place of employment. You will eventually say something incriminating, and there are far more fun ways to get fired :)
What we wish we'd known five years ago
- Never blog about your place of employment
efassor wrote in 
modernwisdom- July 8th, 2009
ecstatic
If, like many people I know, your employer is one of the largest email providers in the world, restricted LJ posts are probably marginally safer.
Two points on this - firstly, email is a little different, aside from your company running checks on the content of your mail all you need to worry about is the security of your own passwords/access/etc. Whereas if a list of people have access to your LJ then any of them could forward it, print it and so forth. Not maliciously, but a lot of people forward amusing rants as a matter of course.
Secondly, believe it or not yes I would also apply that rule to work email. Certainly I would never write a rant to my mother from my work account about hating my job. I also wouldn't use that account to write to my drug dealer if I had one. I also wouldn't blog about drugs, if I took them :) In my mind the principle is the same.
I didn't realise how safe the LJ community felt that locked posts were, and I am a little surprised. But perhaps my paranoia is overkill.