The cake is a lie!!!
(It had to be said...)
Agree, though, that Portal is a great puzzle. It's the first computer game I have purchased, installed, and played in many years. And the install was not easy - it hates antivirus and zonealarm. Still worth the effort IMHO.
There are many amusing videos about Portal, available on YouTube - I particularly like the monologues of the insane AI:http://www.youtube.com/watch?v=mgP4kT5-9Cc
Also try "A Day in the Life of a Turret"http://www.youtube.com/watch?v=Uz5cl131KTk
(warning: some profanity)
And remember, "If at first you don't succeed.... you fail."