So far pretty slick. It doesn’t seem to have broken any of the multimedia plugins and I’m enjoying some of the new features – the theme editor that remembers where you were at last save is long overdue!
As per major new release SOP, there’s an announcement post listing all the new features for 2.9 up at the WordPress Dev Blog (video too).
P.S. Heh, I just added a new category for “wordpress” all in lower case – and the category list autocorrected that to the official capitalised “WordPress”! Warms the cockles of my pedantic little heart, that does.