New articles should be published so that you can target more and more keywords. If you're happy with your current SERP then you can update your site once every 2-3 months. It depends on your competition obviously. Google loves blogs updated daily.
Of course it depends on the goals you have set for your blog but I would say that one time per week is close to a minimum number of times. At 4 times a month I don't know how many people will be drawn to the blog? If it is a new blog I would suggest 4-7 times per week.
Rule says that you should update at least 1 article per day as Google loves fresh content. It will indexed your blog quicker and rank you well. 2 articles per week is also fine.
I notice that nobody uses the internet at the weekend. So best to do between 2 and 5 a week, mon-fri.
Sometimes it is hard to keep up with new articles and new ideas, but 3 times a week is a good medium. I suffer from blog writer's block and I can never come up with anything. I suffer in traffic and clicks from it, so don't be like me. Try to post a new article 3 times a week so you can keep your site updated.
I found this article really useful for keeping the content going: http://www.problogger.net/archives/2009/02/26/7-ways-to-keep-fresh-content-flowing-on-your-blog/
It depends on your objective indeed. Coz there are some people who do the blogging just for fun and treat it like a regular diary. Some people do it for money, of course. If you are in the latest group, i think it should be daily updated.
The general view is that blog needs to be updated atleast once in every two days. But i found some interesting stuff like blogs which were updated nearly 2 years ago still found the top spot in google search. I have written an article on this.
If you have lots of subscribers to your RSS feeds or aim to have lots, each new article makes a certain number visit your site - thereby increasing your traffic. So, the higher the frequency, the more direct traffic you'll get.
There's really no point in ever updating a blog unless you want to target more keywords or you actually have something that you want to say just for the fun of it. It doesn't help with search-engine rankings if that's what you're thinking...
If you are busy, for me once per 2 days is enough. But it's better if you can updates an article per day.
There are no hard and fast rules to determine how often bloggers should post articles. Depending on what type of blog you have, the optimal blog posts per week will vary. Publishing more often may allow you to target a great range and number of keywords for search. Some blogs are update as often as daily, while many blogs are successful in generating traffic with only a few blogs a week. Again it depends on what the goals of your blog are and what viewers you are trying to attract. It’s also important to remember that it’s not all about quantity and frequency (though that can be very important). Providing your readers with quality content can sometimes prove to be more fruitful in promoting your blog than simply continuously publishing articles. Good luck with your blog.