In my opinion, the key to obtaining loyal visitors to your site is to very reliable. If your visitors expect you to update your site on a weekly basis, then you should always do it. If you have a website about news, then you may need to update your site a few times per day. If you go on holidays, then you can leave a message on your site stating that you are going to be gone for a few days. There is nothing wrong with that as long as you engage in dialog with your visitors. Keeping them informed about any important things is crucial.