Details on CSS Changes for IE7
The Internet Explorer team maintains a really good blog here: http://blogs.msdn.com/ie that I recommend subscribing to for useful information.
They recently posted a good blog post detailing some of the CSS changes that have been made with IE 7.0 to enable it to handle CSS better. This is worth bookmarking if/when you are testing your site with IE7 going forward.
Hope this helps,
Scott