One of the coolest and most successful promotions I have seen was conducted by the folks who produce the Jawbone Bluetooth headset.  The Jawbone uses advanced noise cancellation technology and is a well regarded headset although they were too pricey for me the last time I checked into them.  The promotion they were running all week at CES was simple yet effective, anyone who came to their booth and traded in their existing headset got a brand new fully charged Jawbone headset for free.  This was very popular as you might guess and yesterday I dropped in and traded my old headset in for the Jawbone.  It was indeed fully charged which was important as those wearing a headset likely needed to keep doing so before getting to a charging location.  I have only used it for less than a day but I have to say I am very impressed with the quality of the noise cancellation.  For a test I called Kevin on the Jawbone from a tremendously noisy location (I picked it on purpose) and he said he couldn't tell I was on a headset as the audio was crystal clear.  It is a nice headset although a bit bulky and ugly but hey, free is a good price.  :)