Steam put out a new beta UI. It gets rid of the IE integration (uses a webkit based browser I think), reworks the entire layout, and also re-works the Steam Overlay in-game. I think it's pretty awesome, as it's using less memory than before while also being more responsive. The new Library UI interface is interesting, and I like seeing some stats displayed about the games I play.

http://store.steampowered.com/uiupdate/