writes "The Inquirer reports that "The World has come crashing down around Half-Life 2 players today, as Steam's authentication servers in Europe have died."
, and deemzzzz_k
writes "It looks like even Valve wasn't quite prepared for Half Life 2's popularity. HL2 requires registration to unlock the game and although the Valve/Steam homepage claims that it fixed registration issues the servers are still overloaded. Registration is "delayed" and temporarily unlocking the game takes 20-30 minutes over a 1.5MB DSL line."
This seems to primarily be an issue for folks who bought the game from a store; I purchased the game via Steam and was playing at 12:15 am PST on launch day.