The new features are automatic upgrade of plugins, automatic check for their compatibility, image editing integration (Crop, flip, rotate, etc…). Including videos on your posts are also much easier. All you need to do is to paste the video page URL of the supported web sites (youtube, dailymotion, etc…)

The posts are not going to disappear when you accidentally delete them. The new version brings a trash notion where the deleted posts now go there.

Here is a good video of the release!

http://wordpress.tv/2009/12/21/introducing-wordpress-2-9-%E2%80%93-carmen/