For users – you will notice a few things that might catch your eye:

• Easy embeds. Simply copy and paste your a URL from YouTube, etc and it will auto turn it into an embedded video.
• Trash. Now when you have the option to “trash” posts and pages so if you delete something but want to retrieve it later, you can (until you empty the trash)
• Image Editor. Now you can easily manage (crop, resize, etc) your images without using your favorite grpahics program

For developers – here are some of my favorites:

• New custom gallery code that lets you include/exclude items as well as pull in attachments from other posts.
• Post thumbnails. (Just enable and go!)
• Support location of category templates based on ‘category-slug’ (nice especially when you have more than one install with different category IDs
• Added ‘excerpt_more’ filter to wp_trim_excerpt() function, which allow developers to change excerpt ‘[...]‘ more string

You can read more about all the changes and updates that went into 2.9 if you are interested. You can also see all the bug fixes as well.

Download the latest versions of WordPress: WordPress 2.9