- Prevent retry scheduling problems on sites where wp_cron is misbehaving
- Preload mshot previews
- Modernize the widget code
- Fix a bug where comments were not held for moderation during an error condition
- Improve the UX and display when comments are temporarily held due to an error
- Make the Check For Spam button force a retry when comments are held due to an error
- Handle errors caused by an invalid key
- Don’t retry comments that are too old
- Improve error messages when verifying an API key
Source: http://wordpress.org/extend/plugins/akismet/changelog/