Pitfalls of Academic Blogging
First of all, I'm not an academic yet, but I'm planning to be. I read a lot of academic blogs in my field daily or should I say, semi-academic. By semi-academic I mean that they have articles of an academic subject but with more in-layman's-terms approach. And I absolutely love all of them. I believe that being able to explain things simply is an art, not mention extremely valuable, and having a similar blog is something that I aim to do in the future. 

To address your concerns: 


  Maintaining an active blog takes a lot of time and effort. (i.e. it may stop being fun.)


Yes it is. I've been blogging about tech (Android and Linux) in the past and after a while it became an extremely cumbersome experience maintaining a steady flow of news, reviews and opinion articles. BUT this is not what an academic blog is all about. You don't need a good article every day. You need a good quality article once or twice a month. This is not so hard. 


  Fear of failure - many blogs die.


They do. And yours might too. So what? Firstly, you shouldn't fear leaving your blog inactive for a couple of months. This is something you want to do, remember? If you don't have the time or you just don't feel like it for a while just don't do it. If you don't like the view of an abandoned blog after a few months just delete it. It's ok. 


  Being a junior researcher, I worry that people will not care about my blog...


Producing quality content is the key here. If you produce quality articles from which your readers learn stuff you'll find out that after a while a significant amount of them will care. 


  ...or, worse, disagree with what I say.


That's the best part! Being a junior academic you already know that: 


Everything you say must be backed with evidence
No matter the evidence some people will disagree with you


Disagreeing means views and comments. Disagreeing is how you'll make regulars. This is a key concept in blogging. Rarely you will get comments like "I completely agree with your article", not to mention that they don't have a special value. But comments like "I think that you forgot to include the fact that X" sparkle interesting conversations from which both parties learn. 

To answer your questions: 


  Is academic blogging a good idea? Is it worthwhile?


Yes, it's a great idea and it will be worthwhile for you and your readers especially if your articles sparkle interesting conversations. An academic blog indeed increases visibility and creates a more friendly/casual view of the writer which in my opinion most of the times is very much needed. 


  Does it become too much effort?


Not if you limit yourself to one or two articles per month. Your goal is quality, not quantity. You're not a news site, you're an academic. 


  How likely is blog-death?


Very. So what? Just do it. 


  What are pitfalls to watch out for when starting an academic blog?



Do it because you want to do it.
Don't burn yourself out.
Don't get stressed over the quantity. Aim for quality.
Use a simple language.
Be fun.
Have fun.