There is a way to have WMT automatically update the sitemap, but care must be given that you don't allow this to happen too often, say an hour between updating.

Else, upon my findings, you should resubmit every so often. It has also been said that if your navigation is solid enough, Google won't have any problems with it (whatever that refers to.) I learned something from this myself. I didn't know this would need to be anything less than "set it and forget it."

Anyone wanna field this one?