This maintenance and security release fixes almost thirty issues in 3.1, including:
* Some security hardening to media uploads
* Performance improvements
* Fixes for IIS6 support
* Fixes for taxonomy and PATHINFO (/index.php/) permalinks
* Fixes for various query and taxonomy edge cases that caused some plugin compatibility issues
Version 3.1.1 also addresses three security issues discovered by WordPress core developers Jon Cave and Peter Westwood, of our security team. The first hardens CSRF prevention in the media uploader. The second avoids a PHP crash in certain environments when handling devilishly devised links in comments, and the third addresses an XSS flaw.