Valve, Steam and DRM
First of all, there is no allowance made for playing offline. If you don't have an internet connection then you can't play your game, even if it's a single player game that doesn't neccessarily need an internet connection. That is, until Valve decides to make a version of Steam that will work without a network connection.
Now this by itself wouldn't be too bad. Most gamers have DSL or permanent 56K and wouldn't be too fussed by this. But what happens when the network itself becomes overloaded or worse, goes down?
This is exactly what happened the evening Steam was released. The network was just completely overloaded. If you could start a game you were lucky. If you could update your game data to the most recent version you were luckier still. For the past 18 hours the game has been unplayable despite the fact that every person on Steam has a legally licensed copy of Half-Life or Counterstrike which they paid good money for.