I think it comes down to: Do you have something original and substantive to say? If you do, then blogging is a great forum for it. If not, then you'll be lost in the noise and it won't help.
When decided to write my blog I made two rules (which I rarely break): no linking to other blogs just to stroke my ego with an opinion post, no personal experience posts (i.e. today I went to the Taj Mahal and...)
I think the ultimate answer is... it depends. I will say that, if you don't like to write blog posts, you probably should avoid starting a big, echoingly empty blog and just use something like Twitter, or a microblogging engine, or Facebook to establish your online presence. This is kind of why Facebook is there -- to allow folks to express themselves online without having to write entire paragraphs full of interesting and original prose. Not everyone is cut out to be a magazine writer.
The ultimate coward's answer is Linkedin, a site which basically caters to frightened 37-year-olds like me who know they need an online presence but are afraid to actually say anything.
I think having a blog is good for my own career, but unfortunately my blog is really lapsed right now because I find it much more entertaining to reply to posts on news.yc. :)
Reading blogs, however, is more important than writing. I actually got asked in a job interview recently who some of my favorite bloggers were. One I mentioned was joelonsoftware, after which the interviewer told me that their company uses Fogbugz, mainly because they too like Joel's blog. It was a definite good point in the interview :-)
Another thing to keep in mind is that you should only put stuff on the internet that you won't mind people reading years from now, because once it's out there it's out there.
It's nice to put on a business card, but I question whether its mere presence actually makes a difference in selling you to the public. Unless it's regularly updated, it just looks budget...
Either way, if you enjoy writing, just do it!
Blogging is just like any other writing, except with the added caveat that you know people will read it. That makes it so much more motivational than, say, writing a diary, or working on a novel that you suspect you'll never complete.
It's changed my life in ways I can't even describe.
I never can predict what people will like here.
I've found that I better express my thoughts about project in my terrrrrible English.
I think it's because: 1. It's more natural to write about programming in English 2. My English constrain me. And this good =) 3. I need to write less symbols