Some of the out of the box SharePoint page layouts use a
<div id="footer">in the middle of the page. If your custom branded master pages, css, or theme has a style called out for #footer that sets a crazy width or height for your actual site footer it will ALSO apply to this div that is in the middle of the page inside of a table cell. This will end up stretching your entire page and is really difficult to track down.
You have been warned.