Once or twice a week. To be honest, i use adsense just to get more "attention" from spiders and will change to other advertising network in a month or two.
The adsense bot. Your new site will be index in less than a day if you use this trick. Off course, you have to do seo work before inviting spiders to crawl your site and get at least a few quality backlinks from high pr site ( your own network, different ip or third party ).