It is more advisable to update your blogs often... the better it would be if you could update it everyday. As how I read about Search Engine Optimization information, constant updates on your web blogs is also a must.
the best advice for that is to stick on a regular schedule. It doesn't matter if you update every day or every week - your audience will develop expectations. You want to meet those expectations. Don't post 3 times per day for a week, then stop for 3 weeks, then repeat. That just gets your new visitors expecting something that you're not delivering.