The new features are excellent. My favorite is that all widgets are now multi instance, and the widget  management interface is very nicely done.

This WordPress version is named in honor of Chet Baker.  To learn more there is an excellent overview video on the WordPress.org blog – http://wordpress.org/development/2009/06/wordpress-28/

My upgrading advice is as fairly normal in any software upgrade … If you have a rather simple blog using a few well recognized plugins you are likely “safe” to update now.  But if you have a complex WordPress based web/blogsite using a large number of sophisticated plugins I would wait at least 2-3 weeks before upgrading