No change log for this version that I could find, but I am sure it addresses bug fixes and probably some tweaks to increase the speed. If you notice anything new, leave a comment.
Here are some the new features that are offered in App World 3.1:
Gifting/Request a Gift – allows you to request that a friend or family member pay for any application within App World.
Content Rating – allows content providers to rate the maturity level of their content and for you to filter content based on their desired level
WiFi Only Support – will allow App World to still operate when a you only have a WiFi connection
New Language Support – Simplified Chinese, Traditional Chinese, Korean, Thai, Indonesian, Vietnamese, and Dutch