Valve released yet another puzzle website but to do with Portal instead of the last one which was for HL2.
http://www.aperturescience.com/
They made it into a Matrix type MS/DOS program, so far people have figured out a lot of things but to get you started:
Type help for a message.
Or type user and then enter a name and password portal.
Explore the B drive, answer the questions, don't bother memorizing the 64 digit code cause it changes non stop and doesn't get accepted.
Text appears randomly for a split second on pages and spells THECAKEISALIE so type that after logging in to see a camera thing and apart from that people have found a cake image:
Details here:
http://www.hlfallout.net/comments.php?id=8799&type=news&page=1
Enjoy.