Here’s an interesting pro-blogging argument:
Also keep in mind that for every person reading this chapter a poor villager in India is learning SQL and Java. A big salary can evaporate quickly. Hundreds of thousands of American aerospace engineers laid off in the 1970s discovered this. The ones who’d toiled in obscurity on “landing gear bolt #39” ended up as cab drivers or greeters at Walmart. A personal professional reputation, by contrast, is a bit harder to build than the big salary but also harder to lose. If you don’t invest some time in writing (prose, not code), however, you’ll never have any reputation outside your immediate circle of colleagues, who themselves may end up working at McDonald’s and be unable to help you get an engineering job during a recession.
– Philip Greenspun
A little more boring but similar in conclusion paper How to be a leader in your field. Blogs are great tools that make it easy to write about your thoughts and ideas on the web. But never forget: in the end, it’s the quality of your ideas that will make or break your reputation.