ok i know steam can download hl2 for you but would you rather just go to the store and buy a nice set of cd's which won't be that big of an installation hassle or getting it via steam?
steam is sort of a download manager for valve half life products. They released a steam 2.0 beta that is free to the public but you will have to pay for half life 2 when it is available over steam
To put it simply, I don't trust Steam. Now if the Steam purchase allowed you archive the game in its entirety on CD (or, better yet, if Valve sent an official CD copy of the game to you after buying from Steam) then I would go for it, but I don't like the idea of not being able to play my brand new game just because my internet service provider is down for the afternoon.
I don't want to have to run Steam in the background just to play HL2. And since I've already preordered HL2 at EB, I think I'm gonna get it from the store.
I am going to be getting both retail and steam versions.. Steam so I can have it all right as it happens such as updates, add ons and bonus stuff.. And retail for when I can't log onto the net due to server crashes, and for when I want to play Lan with my son or a friend. Heck , I might get 2 steam accounts since i have 3 computers capable of running it.