Hi, I am working on a Guitar Tab site (in spanish) and we are uploading via CMS data everyday... like 200 songs a day... right now i have around 7k songs but this changes everyday. How often would you recommend to resubmit my sitemap ?
Submit it every day if you have new links everyday. Google will never penalize you for doing that, since you are improving the way they will crawl your site. In fact a sitemap helps you, but ir also helps them.
Resubmit, as often as there are changes. You don't have to log into Google's webmaster tools, you can do it via HTTP, just put the correct past to the url below. www.google.com/webmasters/tools/ping?sitemap=http://www.YOURWEBSITE.com/sitemap.xml
If there is good linking in your site, then just "ping" Google (Ispence above) on the hour. Then nightly or every two nights create a new Sitemap. Google will follow any modified page within the site to obtain new pages. Thats why just "pinging" Google works. Creating the Site map for large sites takes time so that is why it should be done nightly.