The new security patches were discovered by WordPress core developers and hardens CSRF prevention in the media uploader. It also adds a patch to avoid a PHP crash in certain environments because of links in comments. The third big patch fixes an XSS flaw in the code.
There are also several other performance improvements and fixes for IIS6 support, fixes for taxonomy and PATHINFO permalinks and fixes for various other query and taxonomy issues caused by plugin compatibility.
I highly recommend that you update your WordPress installation to WordPress 3.1.1 to avoid being affected by these security loopholes.