I bought HL2 about 2 weeks after it came out, and I've never, ever had a problem. I don't understand why everyone is complaining about offline mode. During winter break, my desktop was disconnected from the internet completely(no modem, just 10/100 ethernet, which I don't have at home). Steam started up and told me it couldn't connect to the server. Fine, I pushed the little button that said, "Start Steam in offline mode" and played HL2 without any problems.
I haven't yet had to deal with the CD-Key issue, but since I bought my game online, I probably won't have to. The only annoyance was that I had to wait a day or two to download everything off of Steam, so I couldn't play as soon as I bought it. But I KNEW that was going to happen, so it didn't bother me at all.
As for the case if Valve goes out of business, I'm confident that they will release a patch before they do that frees the user from Steam. It's not such a bad system.
Marsz, marsz, Dąbrowski,
Z ziemi włoskiej do Polski,
Za twoim przewodem
Złączym się z narodem.