Well, Gabe Newell made his acceptance speech at the GDC awards. Near the end of the speech he started to talk about the Portal ARG, then the projector behind him with the computer screen with his slides on it cut to a Windows BSoD. Gabe said "I guess that's what I get for working at Microsoft" then quickly finished his speech and left with a "good luck figuring it out." The live stream of the speech didn't show the projector behind him so it took awhile to figure out what the BSoD said. Eventually pictures were posted and people pieced together what happened.
It started out as a regular Windows BSoD: http://i42.tinypic.com/id7q11.jpg
Then changed to a GLaDOS BSoD: http://i43.tinypic.com/2nj045.jpg
The code in the second one is hex. Someone converted it to decimal, then to another format, which ended up reading:
S U S : P E N D ... U N T ( I ) L ... E E E
aka suspend until E3
So yeah... now we gotta wait till June.