There was a cutoff date for that first promotion, so there are people who pre-ordered the set but did not get the disks. My suggestion is to look through the blogs and find that cut off date, if you ordered before it, then they owe you a pair of disks.
The cutoff date for the free gliding discs was July 27, 2011.
I received the discs with my dvds hoping they would be better than my furniture sliders. I'm kinda disappointed in them, for me they're a little too wide (9" dia.). I prefer the width of my furniture sliders instead (8" long x 5.50" wide).