Anecdotal counterexample: I successfully moved from development into technical writing because I had a blog that a company got in touch with me about and said, "We really like your writing. Have you considered being a technical writer?"

My honest feeling is that if you're a good writer and not just posting ranty flamebait -- and "strongly worded and highly opinionated" is not the same thing, although it can be -- blogging is valuable. Or at least it used to be. And really, I'd like to see it make more of a return, too.