If by what have you done to us you mean, "I'm buying a bunch of them, setting them up around the apartment hooked up to motion sensors, and figuring out how to get from one end to the other without getting shot to death", then yes, what has Valve done to us?
I'm not really doing it, but it sounds so tempting and fun.
EDIT: Damn, didn't see the 4" part. That takes a bit away from the excitement. A little. Not much. Instead I will create rooms out of boxes and setup real life portal levels for action figures to traverse, muahahaha.
Now, if it was a full-size replica for $20....
I just want to get four to make one of these, but I don't have the money.
http://www.thinkwithportals.com/turret_comic/#4
Your kids'll LOVE you for doing that!
Maybe NewEgg can sponsor you?
Probably they do so but it doesn't affects the main ideas.
Read the TOS for rules concerning links in signatures...
Anyone care to squeeze a raspberry pi into one?
Down to $16...
(with $5 shipping. NVM.)