While we’re putting the finishing touches on the new library you can follow the Steam blog for more updates and in-depth information about the new library before we open the public beta on September 17th.
You will probably lose all your categories. I gave up on that the first time steam wiped them out.
Everyone is not able to get this beta if you want to check out the new look.
For those trying out the new look Steam, be warned. The community pages are now shown readily for games you are playing, and they tend to be filed with spoilers and pics from the game you might still be playing.