I wonder how people with so many sites can constantly update their sites.I think even if its only 1 site i would alreadly have to spend so many time marketing and update the content. Any inputs?
Many people pay to have their content updated (paid bloggers, posters, or writers for example) or have their content automatically update via RSS.
There is no simple answer to your question. I have one site which adds over 200 articles per day. I have a couple which hardly every change. However, the more dynamic the site the better. The better the content the better. That latter point not only helps maintain and/or increase the number of repeat visitors, it makes people think they did not waste their time visiting your site. Sourcing good, relevent content is a much harder problem to solve. If you have the money and a good enough income stream, from your site -- whether through advertising or subscriptions -- hiring freelancers is a very good way to get good quality material on a regular basis. If you do not have money to spare, be prepared to work very hard.
I always tried to update my content once a week. At least to make sure that the site is still active so Google bot still come around the site. It's a good way to attract new visitors too.
The optimal is to update your content two times per day, but of course that is not really easy.... But it's cool both for visitors (especially the return visitors) and search engines. As for the second one, I did an experiment with a site of mine, which I stop updating for about 3 weeks and the search engine traffic droped. Then I continue updating the site and the traffic increased.
You ask about updating sites. I see you advertise in yor signature, click on it. It did not take me long to figure out that this is very time consuming. It boils down to cost vs. time. I guess that old addage is right. TIME IS MONEY
Arguably the best way to update site content is a community. Let people update the site for you, you can even get it done for free Example: myspace youtube google edit: ok google is a bad example becuase its not a community, but other people update google's search results!