We've added some new features to the beta today:
Booster packs: Booster packs are additional cards for games that will drop periodically. Anyone who has collected all the trading card drops they can for a game and have used Steam in the last week may receive one of these booster packs. These packs contain three additional cards for the game, and may contain foils. If you receive a booster, you will get a "1 new item in your inventory" alert.
Game Collector Badge: There's a new badge which will grant you XP based on how many games you have in your Steam library. This badge replaces the "100 XP for having at least one product registered" message at the bottom of the badges page.
Profile Game Count: The number shown next to the "Games" link on the new profile should now more closely match the number of games shown in the Steam library.