So the Valve ARG is not over, even after the release of portal 2. There was a new update last night.
The game always referenced the Borealis from Half-Life 2 Episode 2, now it appears to be focusing on it, C.J. is assumed to be Cave Johnson the founder of Aperture science. J.H. is assumed to be the captain of the Borealis.
—LOG FROM [ REDACTED ], BY J.H. TO C.J.—
1. We designed the entire thing to be very, very durable. It was easy to get the materials since everyone’s been thinking
it’s a simple icebreaker ship. Ha.
2. We have made sure to strip it of anything not necessary, so that we have plenty of space for it. It doesn’t have any
backup supplies in the event the crew runs out of food, though. And there isn’t much food onboard in the first place.
3. In the event you need to send it off all of a sudden, use the OR box with code ‘hb1′.
That’s all, C.J. Not much else I can tell you other than this won’t leave a blight on our record. Mesa is going to be sore
when they see what we’ve done.
It looks like (And I hope) that Half-Life 2: Episode 3 will be released in an ARG just like Portal 2. The portal 2 source engine is an update and they've clearly been working on EP3 content for some time now, this seems very plausible.