I installed it yesterday to use whilst developing a theme, I have to say it's bloody brilliant Interface takes some getting used to after being used to a horiztonal navbar for so long, but it's got so many more useful features it's a massive step in the right direction for Wordpress. I love the automatic upgrade and automatic plugin search + install, it's a shame they couldn't do something similar with Theme's as this would make Wordpress 100% idiot proof when combined with scripts like Fantastico for installation
I haven't tried it yet, but from what I've heard, it's going to be a complete overhaul to the admin area and definitely a step in the right direction, as you said.