This is what blogger Seth Goddin says on the subject
I find that I have about six bloggable ideas a day. I also find that writing twice as long a post doesn't increase communication, it usually decreases it. And finally, I found that people get antsy if there are unread posts in their queue.and adds
post only when I have something I really want to say that I think will interest my readers. I try to stay away from the online echo chamber where everyone writes posts about everyone else's posts.
On thing that I would add to Seth's comments though is that frequency will depend upon your motives are for blogging.Whether your blog is mini news aggregator or simply an exchange of ideas will influence your frequency as will time resource.
When for example is the best time to blog,do you post all your blogs in one go or space them out