The lights are on
Entering a special E3 promo code on EA's Origin service unlocks the Close Quarters DLC pack for Battlefield 3.
To get your free content pack, launch Origin and select "Redeem Product Code..." under the Origin menu on the top bar. Enter "BF3E3" (without the quotes) and you should unlock the Close Quarters pack.
Sadly this offer only seems to be good for PC players, but console fans can console themselves with the fact that Close Quarters is our resident Battlefield expert's least favorite content pack for DICE's shooter. Update: Apparently this is free on console as well, so get out there and download yourself some free DLC.
[Thanks to news tipster Michael Anderson for the heads up]