Just thought of something...
A comment mentioning cake has made me think of something. It sounds a bit crazy, but a tiny bit of Portal may have been inspired by the musical/film Sweeny Todd.
The basic plot of Sweeny Todd is
gepy wrote:"The companion toilet cannot speak, however it can take your crap."Journey - no idea on length = don't know the % done
There you really said something to think about... the only difference is that Sweeney Todd's friend had a pie store, and we're talking about cake, not pie. Even tough, there's not a huge difference between cake and pie...
"Duct Tape is the answer."
"The Enrichment Center is required to remind you that you will be baked, and then there will be cake." (subtitles say: "The Enrichment Center is required to remind you that you will be baked [garbled] cake.")
So yes, there is some implication there, that maybe you == cake. From the point of view of an insane machine. 
Its not the first (or only) reference to other books/literature in Portal, its and it would be no suprise to find out that one of the original developers really liked Sweeny Todd. . .
Whats really funny to me is how some aspects of the game (the Weighted Companion Cube, cake, etc) have almost gained a cult status of their own just because of a few chance references in the Portal gameplay. People sure can be odd sometimes; you never know what we will obsess on.
Chell may have developed her own fan base, like our beloved companion cube 
but to me she seemed a bit grumpy, which is maybe why people prefer the cube.
http://upload.wikimedia.org/wikipedia/en/7/7f/Portal_Chell.jpg
gepy wrote:"The companion toilet cannot speak, however it can take your crap."Journey - no idea on length = don't know the % done
but to me she seemed a bit grumpy, which is maybe why people prefer the cube.Wouldnt you be grumpy if you woke up in a glass room, got told to do all these wierd crazy dangerous tests while some insane AI was telling you its impossible and to not die and such?
Nope, I would just get drunk with the Companion Cube
gepy wrote:"The companion toilet cannot speak, however it can take your crap."Journey - no idea on length = don't know the % done
Inspiration can come from anywhere, and sometimes it's not even concious.
I see it with my drawings, sometimes I draw a girl "randomly" and later I recognize that some elements of her clothes and/or body come from movies or anime I saw, sometimes many years before.
And sometimes I don't realize it before I show the drawing online and people say me : she reminds me of <insert name here>
So your theory is very possible. But the funny part is that it might be true without that the valve employee that thought it up actually knows it!
And yes, test subjects may perfectly be an ingredient of the cake. After all, it DOES contain sediment shaped sediment =p
NO! THE CAKE! NOOOOOOOO !