Valve's Erik Johnson has posted a Steam status update on the official Steam forums, mentioning that the beta testing period for the content delivery system is coming to an end. This means that soon, the entire Half-Life userbase will be converted to Steam. Here's what that means

This means that we will be resetting the Steam account database from scratch. After this, you will need to have a valid CD-Key to access games via Steam, so you will want to treat your Steam account as permanent. One CD-Key will grant you access to all of the games currently available in the Steam beta. The Friends database will remain intact, so if you create an account with the same name when the beta ends, you will retain your Friends list. The next step will be to release the remaining three Half-Life 2 movies, fix the remaining issues with the Riot Shield in Counter-Strike, and any remaining issues with Steam. This will happen almost immediately after the Steam beta ends.