In a brief announcement released this evening, Valve stated that Half-Life 2 preloading via its Steam service has finally begun. The announcement explains that "those who have selected the preloading option will have encrypted Half-Life 2 files delivered to their PC. No purchase is required to preload HL2, but it is required to activate the game."
While no further details about the highly sought-after PC shooter's release date is disclosed in the announcement, it specifies to prospective preloaders that "purchase options will be released soon. Then, the moment the game is made available, those who have preloaded and purchased Half-Life 2 via Steam will be authenticated and ready to start playing."
[UPDATE]: GameSpot attempted to begin preloading Half-Life 2 assets throughout last night but consistently encountered the following message: "The Steam servers are currently too busy to handle any more preloads of Half-Life 2. Please try again in a few hours." This morning at about 8:30am PDT, attempts finally succeeded as the preload began. The apparently large amount of data does not take a short time to download, even via a very fast Internet connection. When finished sucking down the hundreds of megabytes, the Steam program prompts, "A locked copy of Half-Life 2 is now on your computer." Anyone got a key?
We'll have more information on Half-Life 2's possibly imminent release as it develops.