its not necessary to post on everyday.. if your blog's followers in bulk quantities then you have to post every day. But if you think that your blog's follower in limited then you have to take 2 to 3 days time period, because if you post everyday then the interest of your follower should be reduce and if you take 2 to 3 days time period and also post a beautiful things then its better then post on everyday.
You have to take to account of how much noise you're making every time you post something. It's perfectly OKAY to post 20 news stories a day if you're a news/technology website if you have a few writers, however it's not okay to do the same on a personal blog. Think of it as if you were looking through your RSS feeds, and the majority of the posts came from one site. You would delete that, just as you would unfollow an annoying person who posted 20 times in 5 minutes on Twitter.
I wouldn't recommend a set posting frequency for anyone else, but I post only four or five times a month. For me at least, blogging is not a full-time occupation, and I believe that maintaining the quality of what I post is far more important. For this reason, some of my posts take a week to put together.
It's your blog, so how often you post is your choice and no one else's.