Reason 1: The number of bloggers is small, and blogging is new. In terms of econ grad student bloggers, there has been me, Steve Randy Waldman, Adam Ozimek, Daniel Kuehn, Kevin Bryan, JW Mason, and maybe one or two others. That's not a statistically large sample, and there are lots of confounding factors (research quality, blog subject matter, etc.). So it's basically impossible to do any kind of quantitative analysis to answer the question.
Reason 2: Very few of the people you annoy will actually inform you of the fact. For example, I've criticized modern macro a lot. Maybe that has annoyed tons of macroeconomists, to the point where they wouldn't consider working with me, hiring me, or allowing my papers into a journal that they refereed. But if so, they're not going to write me emails and say "Hey, I think you're a jerk." They're just going to quietly decide that I'm a jerk, and I'll never know why my paper really got rejected.
So basically, nobody will know for a long time how blogging impacts people's careers. Those of us who have tried it are basically just very tolerant of Knightian uncertainty. In fact, I love uncertainty. In many situations I'd rather try something just to see what happens. I'm the character that gets killed first in every horror movie, but that's fine with me, since life is not generally like a horror movie.
But here are a few reasons to think that blogging won't be as bad for your career as many people fear:
Reason 1: Blogging is great for meeting people. Through blogging, I've met awesome people like Richard Thaler, Eric Brynjolfsson, George Akerlof, James Heckman, Betsy Stevenson, and Roger Farmer, not to mention fellow blogger/economists like Mark Thoma, Tyler Cowen, Alex Tabarrok, Justin Wolfers, Brad DeLong, John Cochrane, Greg Mankiw, Robert Waldmann, Scott Sumner, Steve Williamson, David Andolfatto, and others (I still haven't met Paul Krugman, in case you were wondering). That doesn't mean those people think I'm an elite researcher just because I blog, or will do me any personal career-related favors. Blogs are not a good-ol'-boy network. But it's very helpful to meet this sort of people, to get ideas and perspective, learn how to think about things, and see what's going on in the world of economics. Not to mention networking; senior people advise younger people, and younger people are potential co-authors.
Reason 2: Blogging really doesn't take up much time. It's like any other hobby; it may put a crimp in your social life, but work will still come first. Heavy blogging will require 2 hours a day, but I would say I spend an average of only 20-30 minutes a day on it. And I never feel pressured to post more. Blogging is not a job, so it's not an obligation.
Reason 3: Blogging helps you think. It helps to get things down on paper. Sometimes you have an idea, and then when you start to write it down you realize how vague and/or implausible and/or illogical it is. Writing an idea clarifies the idea, and it helps you practice communicating your idea to others. This will help with writing papers. Even the "blog-fights" help with logical thinking and being able to dissect arguments.
Reason 4: Name recognition is somewhat important in economics, and there is a bit of evidence that blogging helps to build name recognition. This evidence should be taken with several grains of salt, of course, for reasons discussed above.
So there are reasons that blogging might be good for one's career. But these should be viewed simply as mitigating the (unknowable) risks of blogging, not as reasons to start blogging in the first place. The real reason to blog is to affect the national conversation, to get involved with policy and national affairs in some small way, and simply for the sheer joy of thinking about stuff. In other words, the same reasons that people should go into academia in the first place. If your main goal is to make money and wear a suit and have a swank office - and there's absolutely nothing wrong with that - go find a nice safe job in a bank!
Update: In the comments, Steve Williamson adds:
Here's an old blogger perspective. There is risk associated with getting into anything you have not tried before. When you're young you have to take risks, otherwise you never get anywhere. There is risk in blogging just as there is risk in anything else we do. You can say foolish things in a blog post. You can say foolish things when you present a paper at a conference. In the first case you reveal your foolishness to more people, but they are more forgetful. Tomorrow they will move on to another idiot. Old economists who have had some success in the profession and have tenure can coast - they don't have to take risks. But coasting is no fun, and rust never sleeps. If you have tenure, you can use it to your advantage. Offend a few people. Speak your mind. Maybe it matters.Sounds like great advice to me...
Update 2: In the comments, Frances Woolley adds:
Academic publishing is becoming increasingly dysfunctional. People have to publish to get tenure/promotions/government or other funding, so everyone wants to get stuff out, but no one wants to referee for journals or read their contents (except for a dozen or so top journals).
As academic journals lose relevance, conferences, high profile working paper series like the NBER, and blogs are gaining. I get way more eyeballs - and way more ideas out there into the public domain - by blogging than I would by publishing stuff in mid-ranked journals.Interesting...