The answer, of course, depends on you, on how much time you have available and, most of all, on what you want. I began to blog a few months ago and started off posting about once every two weeks. (Little did I know that I was fostering an addiction, but that's a post for another time!) I had no idea if anyone was reading my posts; it felt as though I was tossing them out into a void. Then I found Google Analytics. It was one of those moments where you feel warm light fall on your shoulders and hear the sound of trumpets.
Now at least I knew whether anyone was coming by my site; at that time, about six people a week, but still! That was okay; heck that was great! I was excited that six people were reading my blog.
My excitement lasted for a few days, until I found out hundreds were visiting the blog of a friend of mine. I wanted that kind of readership (I know! Greedy, aren't I?). But what to do? How could I increase readership? I read and studied and schemed. I tried blogging more frequently (once a week), blogging about different topics, I even tried leaving a reader participation 'hook' at the end of my post to encourage feedback. And you know what? It worked! Traffic on my site began to increase and, slowly, even the rate of increase began to increase.
And then it all came crashing down. I was using Wordpress at the time and loved it, especially all the different styles, and then, mysteriously, the site that was hosting my blog died. All that work! All those posts! Everything was gone.
After a fair amount of hand-wringing I decided to start again from scratch. I decided to use Blogger.com this time, so I wouldn't have to deal with any technical glitches, and because it was easy to customize and was free (love free!). This blog would be about everything and anything to do with writing, with a special focus on topics relevant to people at the beginning of their writing careers.
Today, although I can only dream about Joe Konrath's numbers, I'm happy to be able to write that more than six people read my blog, but I only saw a significant increase in numbers after I began to blog four or so times a week. That said, I think that the number of posts it takes to start to build a platform likely differs for different people and different blogging styles. John Locke, for instance, advises blogging once a month and that strategy certainly has worked for him.
If you are wondering how often you should blog, I sincerely hope you find out what works for you and, most of all, I hope you find the journey enjoyable.