I too opted into the beta like a month or so ago - the look of the ui itself is better imo and when you right click steam down in the tray area it will show icons for games instead of just names now
the only thing I've noticed so far that kinda bothers me is when you get an achievement it no longer says "achievement unlocked" with the achievement name - instead now it just pops the achievement name and description. okay I like that it shows the description of said achievement now when you unlock it but why get rid of the words "achievement unlocked" ?!