If you have a Google Apps Site created in Google Apps For Teams your account will be officially shutting down on September 4, 2012. Here is a link to the official google apps for teams administration help page filled with all the information of what you need to do.
"Make sure to follow the instructions ... to copy your sites before October 15, 2012. If you do not copy your sites before October 15, 2012, you will lose access to all data in your sites."
There are, however, a couple of 'gotchas' that don't appear to be mentioned.
For the first two items (and also to avoid automatic Site disablements for TOC violations which seem to be an issue for some personal Sites users) I highly recommend using Google Apps for business (free for up to 10 users) and creating/transferring your Sites in Google Apps. See: https://www.google.com/a/cpanel/standard/new3
If you do not already have a domain, you can sign up for one for just $10 / year.
It is easy to move any Site to Google Apps. See http://www.steegle.com/websites/google-sites-howtos/import-site-google-apps
At the moment there is no easy fix for the URL list items issue.