Steam app opens for the general public, unofficial ones booted from Android Market
It is meant for accessing the Steam community and will allow users on both mobile platforms to chat with their buddies on Steam, read the latest gaming news and reviews, as well as follow Steam sales, browse the community groups and user profiles. So follow the source link to log in and start Steam-ing.
For better or worse, unofficial Steam apps, like Steam for Android, SteamDroid and SteamFriends seem to be booted off the Android ship, most likely because of a Valve request, as the company understandably wants you to only use the real deal.
source: Steam (Android Market) & Androinica