This has been posted a couple times today. The site owner doesn't match Valve and the logo doesn't match the one from the Half-Life 3 shirt. Plus, I think it's almost dismissible at face value just because it would be such a ridiculous way to announce the game. Valve loves their big announcements and they love their ARGs. They don't appear to love giant logos on silly sites named "Black-Aperture" (yeah, let's get a little more heavy-handed with the much-vaunted-but-often-debunked HL3/Portal connection, eh? They've said that they want to limit the references between the series to just easter eggs. The Borealis came from Aperture. Aperture occasionally references Black Mesa, etc. No big, direct crossovers.)
This reeks of hoax.